CN1262341A - Computer controlled ion nitrizing process and equipment with plasma source - Google Patents

Abstract

A computer controlled ion nitrizing process and equipment with plasma source is disclosed. Said process includes such steps as heating, keeping temp constant, cooling and ion implantation. Said equipment is composed of power supply system, gas supply system, vacuumizing system and main vacuum chamber. It features that self-heating workpiece is used and computer is used to automatically control the repeation frequency, duty ratio and amplitude of positive and negative pulses pair.Its advantages are simple equipment, low energy consumption decreased by 40%, full automation, stable technology, no annealing of workpiece,and high safety and reliability.

Description

The Plasma Source Ion Nitrided Processes and apparatus that computerizeds control

The present invention relates to ionitriding technology, belong to the material surface modifying technology field.

Nitridation process is the important means of material surface strengthening, at present, state-of-the-art nitridation process is a using plasma source ion nitridation process, this technology generally includes following three contents: the workpiece that 1. will desire nitriding places in the vacuum chamber, fill after vacuumizing with hypobaric nitrogen, by certain discharge mechanism, make the generation nitrogen plasma afterwards; 2. start the well heater that is placed in the workpiece side and make it, regulate heater power with the control workpiece temperature to the workpiece heating; 3. to adding direct current or pulsed negative bias on the workpiece, ooze to attract positive ion in the nitrogen plasma that workpiece surface is annotated.Prior art is in realizing this technological process, exist two subject matters: 1. adopt heater-type heater heats workpiece, this is not only concerning complex-shaped workpiece, heating is difficult to evenly, and, well heater the complicacy that has increased system is set, and the article on plasma body space forms certain interference and pollution; 2. Plasma Source Ion Nitrided technology is the control process of a multiparameter, these parameters have: plasma density, plasma electron energy distribution function, working gas pressure, workpiece bias parameter, nitrogen ion current density, nitriding temperature, nitriding time and notes nitriding total dose etc., for the adjusting of these parameters, prior art is finished by manual method.This manual shift method, randomness is very big, becomes at any time, varies with each individual, and therefore, is difficult to ensure the repeatability of technology, and needs operator to concentrate, and monitors at any time, has increased labour intensity.

Purpose of the present invention and task are will overcome prior art in nitriding process, the interference, the pollution that 1. need heater-type well heater and the system complexity of bringing thus and article on plasma body space to form; 2. the multi parametric process of article on plasma body source ionitriding technology needs manual monitoring, can not realize the deficiency of control automatically, and a kind of method that need not to settle well heater and adopt the autothermal heated parts proposed, adopt the automatic monitoring process process of computer simultaneously, make Plasma Source Ion Nitrided become a kind of full automatic technological process, special proposition technology solution of the present invention.

In nitriding process, workpiece need add a series of negative bias pulses, the positive nitrogen ion pair workpiece surface of negative pulse attraction is annotated and is oozed, simultaneously because the effect of negative bias pulse, make ion obtain kinetic energy, the bombardment workpiece surface, kinetic energy is converted into heat energy, workpiece temperature is raise, if the heat of reasons such as the heat that produces during ion bombardment and thermal radiation loss equates that then workpiece can maintain a certain temperature-resistant, obvious, the heat energy and the pulse-repetition of workpiece that ion bombardment brings in unit time, pulse amplitude and dutycycle are relevant.

In order further to talk clearly this relation, to realize the purpose of control fully automatically, at first explanation is from heating principle.When " immersion " treated that in plasma body the workpiece of nitriding treatment adds pulsed negative bias, its surface just formed a sheath layer, and according to molecular motion scientific principle opinion as can be known, the number of ions of beating at unit surface sheath laminar surface in the unit time is: $\frac{1}{4}{n}_i{\stackrel{\‾}{v}}_i$

Wherein ni is an ion density, and vi is an ion thermal motion V-bar, and under the situation of negative bias, these positive ions all can pass the sheath layer and reach workpiece surface, so, enter the ion current density j of workpiece surface _iFor $j_i=\frac{1}{4}{\mathrm{en}}_i{\stackrel{\‾}{v}}_i=\frac{1}{4}{\mathrm{en}}_i{({\mathrm{kT}}_i/m_i)}^{\frac{1}{2}}$

Wherein e is a unit charge, kT _iBe ion temperature, m _iBe mass of ion.

Because the time of setting up the sheath layer is generally less than 1 μ s, little more a lot of than negative pulse width, so can ignore the variation of sheath layer formation process intermediate ion current density, think during negative pulse, ion current density is j _i

If the negative pulse frequency is f, pulsewidth is τ ₂, average ion current density j then _iFor:

If the pulsed negative bias amplitude is V ₂, the power density p that produces of ion bombardment workpiece surface then _iFor: $p_i={\stackrel{\‾}{j}}_i\·V_2=\frac{1}{4}{\mathrm{en}}_i{\mathrm{f\τ}}_2{V}_2{({\mathrm{kT}}_i/m_i)}^{\frac{1}{2}}$

If the surface-area that workpiece is exposed in the plasma body is S, the power P that produces of ion bombardment then _iFor: $P_i={\stackrel{\‾}{j}}_i{V}_2\·S=\frac{1}{4}{\mathrm{en}}_i{\mathrm{f\τ}}_{2}S{({\mathrm{kT}}_i/m_i)}^{\frac{1}{2}}$

Obviously, to a definite workpiece, promptly S is certain, under specific plasma parameter condition, i.e. and n _i, kT _i, m _iNecessarily, regulate the repetition rate f of negative pulse, pulsewidth τ ₂With amplitude V ₂, promptly may command is injected the total power of workpiece.

When workpiece adds positive pulse, will cause the electron-bombardment workpiece, pulsed electron current density j _eCan be calculated as follows: $j_e=\frac{1}{4}{\mathrm{en}}_e{\stackrel{\‾}{v}}_e$

Wherein, n _eBe electron density, v _eBe electronics thermal motion V-bar, be similar to the situation of negative pulse, can derive draws average electron current density j _e, electronic heating power density p _eWith electronic heating total power P _eFormula: ${\stackrel{\‾}{j}}_e=\frac{1}{4}{\mathrm{en}}_e{\mathrm{f\τ}}_l{\left({\mathrm{kT}}_e\right)}^{\frac{1}{2}}$ $p_e=\frac{1}{4}{\mathrm{en}}_e{\mathrm{f\τ}}_l{V}_l{\left({\mathrm{kT}}_e\right)}^{\frac{1}{2}}$ $p_e=\frac{1}{4}{\mathrm{en}}_e{\mathrm{f\τ}}_l{V}_{l}S{\left({\mathrm{kT}}_e\right)}^{\frac{1}{2}}$

τ in the formula ₁Be positive pulse width, V ₁Be positive pulse amplitude, kT _eBe electronic temp

Because v _e＞＞vi

So j _e＞＞j _i

Be that positive pulse has the heating power more much bigger than negative pulse, generally big approximately two magnitudes, this temperature rise period to big workpiece is meaningful especially.

Hence one can see that, and nitrogenize satisfies it respectively by regulating ion bombardment power and electron-bombardment power in temperature rise period, holding stage and the temperature-fall period of actually operating:

1. temperature rise period:

2. holding stage:

The power loss that ion bombardment power=thermal radiation etc. causes

3. temperature-fall period:

Be not difficult to find out that if the power loss that ion bombardment power＜thermal radiation etc. cause, so, system just is in temperature-fall period.

Obviously,

Be the naturally cooling speed that stops ion bombardment.

Therefore, whole nitridation process can be controlled the temperature of workpiece by repetition rate, pulsewidth and the amplitude of regulating positive negative pulse stuffing.The computerized control ultimate principle of nitriding process that Here it is.

For the less workpiece of size, the three phases of nitrogenize all can be realized temperature control by the adjusting to the negative bias pulse parameter; But,,,, only, do not reach required temperature rise rate sometimes, so also adopt electron-bombardment to improve the workpiece temperature rise rate by ion bombardment in the temperature rise period because its thermal capacity is bigger for big workpiece.Here it is will be by adopting positive and negative bias pulse to realizing.

Basic design of the present invention is to remove the heater-type well heater, adopt the autothermal heated parts of ion/electron-bombardment workpiece, adopt positive and negative bias pulse right, by regulating its repetition rate and dutycycle separately and amplitude with the nitriding temperature curvilinear motion of controlled temperature along setting, follow back the detection workpiece temperature with computer, and in computer, detected value and set(ting)value are compared, make detected value be tending towards set(ting)value or near set(ting)value, swing, temperature control software adopts multiparameter proportion integration differentiation PID control techniques, total notes nitriding dosage that the workpiece per surface area is obtained is to read the workpiece total current by computer with certain frequency, negative bias pulse width and the negative counting under each width are also pressed given equation and are calculated.For safety, also be provided with arc stream discrimination system and feedback control circuit in the system.

The Plasma Source Ion Nitrided Processes and apparatus that computerizeds control proposed by the invention, its technology comprises the intensification of setting, insulation and temperature-fall period and ion implanting process is characterized in that: adopt the autothermal heated parts, promptly utilize the energy heated parts of ion/electron-bombardment workpiece; Workpiece heats up, the temperature control of insulation and temperature-fall period, it is the temperature of recently regulating workpiece by frequency, amplitude and the duty of regulating the workpiece negative bias, for big workpiece for reaching desired temperature rise rate, also adopt electron-bombardment, at this moment, should be by adopting positive and negative bias pulse to realizing, positive negative pulse stuffing is to there being identical repetition rate, the time of its appearance staggers fully and certain time interval is arranged, and its amplitude and dutycycle can be distinguished independent regulation, and during adjusting, positive negative pulse stuffing should satisfy following relation to repetition rate T: $T=\frac{1}{f}={\mathrm{\&tau;}}_1+{\mathrm{\&tau;}}_2+\mathrm{\&tau;}+\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="A9910156800141.png"\; state="\{\{state\}\}">t</figure-callout>}}_1+\mathrm{\&Delta;}{t}_2$ τ wherein ₁Be positive pulse width, τ ₂Be negative pulse width, τ is τ ₁, τ ₂But holding time, Δ t ₁Be the interval of positive pulse and negative pulse, Δ t ₂Be the minimum interval between negative pulse and the positive pulse, by regulating the right repetition rate of positive negative pulse stuffing and separately dutycycle and amplitude, the temperature that can make workpiece is in certain limit of error, along the nitriding temperature curvilinear motion of setting, generally speaking, the amplitude in insulation, temperature-fall period positive pulse all is taken as zero; The workpiece per surface area obtains total notes nitriding dosage D, is that computer reads workpiece total current, negative bias pulse width and the negative counting under each width with certain frequency, and is calculated as follows: $D=\frac{(1+\mathrm{\&eta;})}{e(1+\mathrm{\&gamma;})}(\underset{i}{\mathrm{\&Sigma;}}{I}_i\underset{j}{\overset{J\left(i\right)}{\mathrm{\&Sigma;}}}{\mathrm{\&tau;}}_{\mathrm{ij}}\&bull;n_{\mathrm{ij}})+\mathrm{\&alpha;}{T}_0$ Wherein, η is a nitrogen molecule ion proportion in the nitrogen plasma, and e is an elementary charge; γ is a target, i.e. the secondary electron yield of workpiece, I _iBe i value of workpiece total current, τ _IjFor at same I _iJ negative bias pulse width values under the situation, n _IjFor at negative bias pwm value τ _IjThe counting of following negative bias pulse, α are to annotating the rate constant that nitriding has certain contribution, T when considering the workpiece no-bias ₀Be the total time of workpiece no-bias, can be calculated as follows usually: $T_0=\underset{k}{\mathrm{\&Sigma;}}{n}_k({\mathrm{\&tau;}}_k+\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="A9910156800141.png"\; state="\{\{state\}\}">t</figure-callout>}}_1+\mathrm{\&Delta;}{t}_2)$ Wherein, τ _kBe k the value of τ, n _kFor τ gets τ _kNumber; Workpiece temperature follows back detection in the nitridation process process, the positive negative pulse stuffing parameter control, annotate the calculating of nitriding dosage, finish by computer, temperature control software adopts multiparameter proportion integration differentiation PID control techniques, by the comparison of detected value in the computer and nitriding temperature curve or set(ting)value, and then adjusts the bias pulse frequency, dutycycle and amplitude make detected value be tending towards set(ting)value, or swing near set(ting)value; Processing step of the present invention is:

The first step workpiece is prepared

The workpiece of desiring nitriding is cleared up, and generally is to be immersed in to use ultrasonic cleaning, airing then in the scavenging solution;

Second the step shove charge, vacuumize, inflated with nitrogen

With the workpiece of airing, be placed on the work piece platform in the main vacuum chamber, close vacuum chamber, be evacuated to 1 * 10 ^-2Pa～1 * 10 ^-4Pa is generally 2 * 10 ^-3Pa then, by mass flowmeter nitrogen injection in vacuum chamber, makes indoor really air pressure reach 1Pa～1 * 10 ^-2Pa is generally 8 * 10 ^-2Pa;

The excitation of the 3rd step produces plasma body

Connect power supply, utilize direct current glow discharge, or radio frequency glow discharge, or microwave ECR discharge excitation around workpiece produces plasma body;

The 4th step started automatic nitriding sequence of control

Open positive negative pulse stuffing power supply and computer control system power supply, start automatic nitriding sequence of control, select or set the nitriding temperature curve, so computer is just by multiparameter proportion integration differentiation PID control principle, adjust the parameter of positive negative pulse stuffing, make actual nitriding temperature along the nitriding temperature curvilinear motion, until crossing EP (end of program), in case of unusual, system reports to the police automatically, and prompting is fixed a breakdown;

The 5th step shutdown, sampling, quality and Performance Detection

Behind the end of processing, auto stop, can take a sample this moment, and detect, and generally carries out the conventional metallographic and the detection of aspect of performance.

It is further characterized in that processing method of the present invention, and its positive negative pulse stuffing is produced by supervisory circuit being under computer control, and the right repetition rate of pulse is f, and its scope is 1kHz～20kHz, and positive pulse width is τ ₁, its scope is

-Δ t ₂, be generally 50 μ s～1ms, amplitude V ₁, its scope is 500V～3000V, at holding stage and temperature-fall period τ ₁=0, promptly there is not positive pulse.The negative pulse plating is τ ₂, its scope is , being generally 50 μ s～1ms, amplitude is V ₂, its scope is-500V～3000V, and Δ t ₁=Δ t ₂=1 μ s is advisable.

In general, selecting for use of frequency is relevant with the shape for the treatment of the nitrogenize workpiece, to having the workpiece at rib corner angle angle, will select higher frequency for use for avoiding the starting the arc; The deposition of energy depends primarily on pulse amplitude and dutycycle, therefore in the temperature rise period, and V ₁, V ₂, τ ₁, τ ₂All get higher value or maximum value, at holding stage and temperature-fall period, τ ₁=0, promptly there is not positive pulse, V ₂, τ ₂Get smaller value or minimum value.

In order to realize the technical scheme of the Plasma Source Ion Nitrided Processes and apparatus that computerizeds control proposed by the invention, the equipment that it adopted comprises main vacuum chamber [21], work piece platform [22], pumped vacuum systems [26], airing system [27], power supply system [28] and microwave source system [29], it is characterized in that: main vacuum chamber [21] is made of the garden cylindrical shell, arranged outside at its housing has many little permanent-magnet blocks [20], the polarity of these magnet pieces alternately changes according to certain rules arranges, constitute multipole cusp field structure, article on plasma body magnetize effect of contraction, in order to improve plasma density in the vacuum chamber, and improve its homogeneity, in main vacuum chamber [21] housing both sides, be provided with two electron cyclotron resonace ECR reaction chambers [18], they and UNICOM of main vacuum chamber, around the ECR reaction chamber, be provided with ECR magneticfield coil [19], be provided with vacuum pump interface [24] in the main vacuum chamber bottom, the main vacuum chamber side is provided with hermatic door [23], the desirable part etc. of knocking off, automatically nitriding supervisory circuit [25] is joined by computer interface circuit [13] and microcomputer [14], and microwave [15] is introduced ECR reaction chamber [18] by the quartz window [17] that seals.

Present device is further characterized in that: by regulating solenoid [19] electric current, make near the outlet of ECR reaction chamber and can produce and the corresponding resonant field intensity of microwave frequency, if microwave frequency is 2.45GHz, then producing the required magnetic strength intensity of electron cyclotron resonace is 875 Gausses, the Surface field intensity of permanent magnet is 1500～2500 Gausses, be generally about 2000 Gausses, after seeing through the magnetism-free stainless steel locular wall, decay to 100～700 Gausses at the locular wall inner surface, be generally about 400 Gausses.

Corresponding different microwave frequencies needs different resonant field intensity, if microwave frequency is fixed, then resonant field intensity is also fixing.Equally, the Surface field intensity of permanent-magnet block also is fixed, therefore, behind the magnetism-free stainless steel locular wall of determining, also will decay to a magneticstrength of determining in the locular wall inboard.When frequency is the microwave [15] of 2.45GHz, behind quartz window [17] introducing ECR reaction chamber [18], can generate highdensity nitrogen plasma by the electron cyclotron resonace excitation at 875 Gauss places, because the diffusion nitrogen plasma just can be full of whole main vacuum chamber, at this moment, supervisory circuit [25] is produced just/the negative pulse bias voltage is added on the workpiece [1], can begin nitriding treatment, in nitridation process, computer software is adjusted right frequency f of positive negative pulse stuffing and amplitude V separately automatically ₁, V ₂With pulsewidth τ ₁, τ ₂, make the temperature nitriding temperature curvilinear motion that the edge is set in certain limit of error of workpiece, thereby, nitriding process fully automatically finished.

The technical scheme major advantage of the Plasma Source Ion Nitrided Processes and apparatus that computerizeds control proposed by the invention is: 1. because equipment has removed well heater, adopted from heating mode, therefore, not only simplified equipment, and, improved workpiece plasmoid on every side, made homogeneous heating, better effects if; 2. in computer-controlled nitridation process, computer program carries out multiparameter proportion integration differentiation PID control according to the temperature curve of setting, and feedback response is fast, the control accuracy height, but be a kind of iterative process of automatization, be particularly suitable for industrial applying; But 3. because the actual temperature of computer detail record workpiece, the workpiece total current, the change histories of frequency, amplitude and dutycycle that positive negative pulse stuffing is right, therefore, computer can provide the total notes penetration enhancer amount of workpiece and the change curve of workpiece total current, and this provides reliable data for estimating the nitriding effect; 4. computer-controlled nitridation process is not struck sparks, the not starting the arc, is not caused workpiece annealing, is a kind of safe process operation; 5. owing to removed well heater, can save power consumption about 40%.

Be the description of the drawings below

Fig. 1 is that the present invention is added on the positive negative pulse stuffing of workpiece to structural representation

Right by the positive negative pulse stuffing that supervisory circuit produced under computer control, have identical repetition rate, positive negative pulse stuffing staggers in time fully, each other and certain time interval, the width of positive pulse are arranged is τ ₁, amplitude is V ₁, get τ at insulation and temperature-fall period ₁=0, promptly there is not positive pulse.The width of negative pulse is τ ₂, amplitude is V ₂, τ is τ ₁, τ ₂The adjusting surplus, i.e. τ ₁, τ ₂But holding time, during adjusting, the right repetition rate T of positive negative pulse stuffing should satisfy: $T=\frac{1}{f}={\mathrm{\&tau;}}_1+{\mathrm{\&tau;}}_2+\mathrm{\&tau;}+\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="A9910156800141.png"\; state="\{\{state\}\}">t</figure-callout>}}_1+\mathrm{\&Delta;}{t}_2$

Fig. 2 is the structural representation that the present invention is used for automatic nitriding supervisory circuit [25].Frame of broken lines is supervisory circuit [25] with interior part

The effect of this circuit is temperature and other operating parameters of monitoring workpiece at any time on the one hand, is the control signal of receiving computer on the other hand, by the adjusting of the right frequency of positive negative pulse stuffing, pulsewidth and pulse amplitude, realizes the control to workpiece temperature etc.

Be close to the thermopair on the workpiece [1] of desiring nitrogenize, temperature signal is delivered to isolation amplifier [2], the effect of isolation amplifier is that the bias voltage on the workpiece is kept apart, make it to reach computer interface [13] circuit, and temperature signal can only be passed to computer interface [13], computer is to send frequency f, the pulsewidth τ of three way moulds conversion D/A signal to control negative pulse respectively by computer interface [13] to the control of negative pulse ₂With pulse amplitude a ₂, [4] are electric voltage frequency conversion VFC circuit, [5] are time delay circuit, make negative pulse finish back elapsed time Δ t in positive pulse ₁Delay after just produce, with the stable work of safeguards system, [6] be that voltage pulse-width conversion circuit, [7] are driving circuit, it all carries out power magnification through the pulse signal of having adjusted with frequency and pulsewidth, so that driving pulse modulator IGBT[8], [9] be the numerical control direct supply, its output amplitude is subjected to the D/A signal a of computer ₂Control, the output of the direct current of numerical control direct supply [9] is through IGBT[8] after the modulation, export the one group input coil of powerful pulse signal to pulse transformer [3], and produce negative pulse at the power winding internal induction and be added on the workpiece [1].The generation of positive pulse and negative pulse all fours, its polar are not both that difference coupling phase place by pulse transformer [3] primary and secondary coil realizes.Current sensor [12] can record workpiece ion(ic)current I ₂With electronic current I ₁Machine interface [13] is sent into computer as calculated; comparer [11] is also delivered in the output of current sensor [12] simultaneously; if the workpiece electric current is greater than a certain threshold value, and comparer [11] just has signal to export feedback control circuit [10] to, realizes the defense controls to numerical control direct supply [9].Voltage pulse-width conversion circuit [6], the pulse of output are also delivered to computer interface [13] and are carried out pulse counting, i.e. n except that sending driving circuit [7] ₁, n ₂, so realize supervisory function bit.

Fig. 3 is the designed Plasma Source Ion Nitrided device structure synoptic diagram that computerizeds control of the present invention

The outside of the garden column main vacuum chamber [21] that makes of stainless steel is placed with a lot of fritter permanent magnets [20], its polarity alternately changes ground according to certain rules and arranges, constitute multipole cusp field structure, indoor plasma body is played effect of contraction, the mechanical pump that is connected bleeding point [24] is communicated with main vacuum chamber with the molecular pump system, be provided with nitrogen inlet [16] in the end of ECR reaction chamber [18], in the inflation gas circuit, dispose mass-flow gas meter, in order to regulate air inlet speed, both sides in main vacuum chamber [21], be provided with the electron cyclotron resonace ECR reaction chamber [18] of two band quartz windows [17], be communicated with main vacuum chamber [21], the arranged outside of electron cyclotron resonace ECR reactor [18] has ECR magneticfield coil [19], by the regulating winding electric current, can produce 875 gauss magnetic fields in ECR reaction chamber [18] exit.Frequency is the microwave [15] of 2.45GHz, by the quartz window [17] that seals, after introducing the ECR reaction chamber, can be at 875 Gauss places, eject highdensity nitrogen plasma by electron cyclotron resonace, because the diffusion plasma body just can be full of whole main vacuum chamber, at this moment, with supervisory circuit [25] produce just/the negative pulse bias voltage is added on the workpiece [1].Just can begin nitriding treatment, workpiece [1] is to be placed on the work piece platform [22], work piece platform [22] is joined with computer [14] by supervisory circuit [25] and computer interface circuit [13], computer software is adjusted the right frequency of positive negative pulse stuffing automatically, and separately amplitude and pulsewidth, make the temperature nitriding temperature curvilinear motion that the edge is set in certain limit of error of workpiece, thereby fully automatically finish nitriding process.Symbol [23] is main vacuum chamber's hermatic door.Frame of broken lines with interior be system of main vacuum chamber [30].The direction of arrow that symbol among the figure [15] is indicated is the microwave approach axis; The direction of arrow that symbol [16] is indicated is the nitrogen inlet direction; The direction of arrow that symbol [24] is indicated is the direction of bleeding.

Fig. 4 is the designed Plasma Source Ion Nitrided device systems synoptic diagram that computerizeds control of the present invention, system of main vacuum chamber [30] is furnished with power supply system [28], airing system [27], pumped vacuum systems [26] and microwave source system [29], computer machine [14] links to each other with supervisory circuit [25] by computer interface circuit [13], thereby nitriding process is monitored automatically.

Fig. 5 is the computer controlled automatic programflow chart of technology of the present invention, and arrow is the progress direction of flow process among the figure.Automatically after the nitrogenize program start, at first set temperature rise rate a, keep temperature T _H, nitrogenize required dosage D ₀, rate of temperature fall b and end temp T; So nitriding temperature curve T _c(t) can be expressed as

Here T ₀The expression room temperature.Undoubtedly, also can set the nitrogenize curve of other formation.Then nitrogenize begins, and excitation produces nitrogen plasma, time zero clearing; In the temperature rise period, cycle detection workpiece actual temperature T _m(t), and with it and T _c(t) relatively,, carry out multiparameter PID and regulate, promptly regulate the right frequency of positive negative pulse stuffing and separately width and amplitude, difference is reduced, up to T according to the difference of the two _m(t) 〉=T _H, promptly reach T _c(t) in the value of holding stage, change holding stage this moment over to; At holding stage, the actual temperature T of the cycle detection workpiece that remains unchanged _m(t), and with it and T _c(t) relatively, carry out multiparameter PID according to the difference of the two and regulate, difference is reduced; Workpiece total current during the negative pulse is carried out track record, to the negative pulse width under each workpiece total current, and record is carried out in the pulse counting under each negative pulse width, simultaneously also the τ value is carried out track record, computer utilizes aforementioned formula to calculate the nitrogenize dosage D (t) that workpiece received according to these numerical value, until D (t) 〉=D ₀, promptly reaching the nitrogenize dosage of expection, change temperature-fall period this moment over to, and the time is zero setting again; At temperature-fall period, the actual temperature T of the cycle detection workpiece that remains unchanged _m(t), and with it and T _c(t) relatively, carry out multiparameter PID according to the difference of the two and regulate, difference is reduced, until T _m(t)≤and T, nitrogenize finishes.

Further specify details of the present invention below in conjunction with specific embodiment.

A Cr18Ni9Ti stainless steel rotating shaft that is used on the piston ring cleaning machine is of a size of 35 * 280 millimeters of , requires surface abrasion resistance, and has erosion resistance, adopts the technology of the present invention to carry out nitriding treatment, and step is as follows:

The first step workpiece cleaning

Workpiece is put into Ultrasonic Cleaners, adds scavenging solution, opens ultrasonic wave, cleans 15 minutes, after the taking-up, cleans with acetone is cotton, cleans with the raw spirit cotton, at last airing in air again.

Second the step pack into workpiece, vacuumize

Workpiece is packed in the main vacuum chamber of the Plasma Source Ion Nitrided equipment that the present invention computerizeds control on the work piece platform, close door for vacuum chamber, open mechanical pump and molecular pump in succession, make the vacuum chamber base vacuum reach 2 * 10 ^-3Pa.

The 3rd step microwave ECR excitation nitrogen plasma

In vacuum chamber, charge into nitrogen by mass flowmeter, make its air pressure reach 8 * 10 ^-2Pa; Open the power supply of magneticfield coil, regulating winding electric current, the magnetic field that makes ECR reaction chamber exit produce 875 Gausses this moment; Then open frequency is the microwave source of 2.45GHz, regulates its power and exports 630 watts to, and at this moment, the lilac aura that sends from ECR reaction chamber and main vacuum chamber nitrogen plasma as can be known has been full of main vacuum chamber.Recording plasma density with the Langmuir probe is 2.3 * 10 ¹⁰/ centimetre ³, electronic temp is 6.2eV.

The 4th step started automatic nitriding program

Open supervisory circuit power supply and positive and negative direct supply, start automatic nitriding program after, screen is the display parameter setting interface.Set a=1 ℃/second of temperature rise rate, rate of temperature fall b=0.2 ℃/second, holding stage temperature T at this _H=400 ℃, nitrogenize dosage D ₀=4 * 10 ²¹/ cm ², end temp T=60 ℃, after mouse click " affirmation ", program promptly entered the temperature rise period, changed holding stage approximately over to through 6 minutes, and holding stage continues to change temperature-fall period automatically over to after 4 hours, and temperature-fall period continues half an hour approximately, and nitrogenize finishes, auto stop.

The 5th step quality inspection

The metallographicinspection surface has generated the nitride layer of thick about 6 μ m.

Microhardness checks that surface hardness is 724HV under 25g load.

The small angle X-ray diffraction analysis and observation has arrived 5 γ from nitride layer supersaturation nitrogen austenitic phase _NThe peak.

Electrochemical corrosion test shows that through about 4 hours nitriding treatment, surperficial corrosion resistance does not become.

Claims (4)

1. the Plasma Source Ion Nitrided Processes and apparatus that computerizeds control, its technology comprise intensification, insulation and temperature-fall period and ion implanting process, it is characterized in that:

A) adopt the self-heating type heated parts, promptly utilize the energy heated parts of ion/electron-bombardment workpiece,

B) workpiece heats up, temperature control in insulation and the temperature-fall period, it is the temperature of recently regulating workpiece by frequency, amplitude and the duty of regulating the workpiece negative bias, for big workpiece, for reaching desired temperature rise rate, also adopt electron-bombardment, at this moment, should be by adopting positive and negative bias pulse to realizing that positive negative pulse stuffing is to there being identical repetition rate f, the time of its appearance staggers fully, and certain time interval arranged, and its amplitude and dutycycle can be distinguished independent regulation, and during adjusting, the right period T of positive negative pulse stuffing should satisfy: $T=\frac{1}{f}={\mathrm{\&tau;}}_1+{\mathrm{\&tau;}}_2+\mathrm{\&tau;}+\mathrm{\&Delta;}{t}_1+\mathrm{\&Delta;}{t}_2$

By regulating temperature that right repetition rate of positive negative pulse stuffing and dutycycle separately and amplitude can make workpiece in certain limit of error, along specific nitriding temperature curvilinear motion, generally speaking, the width of insulation, temperature-fall period positive pulse all is taken as zero,

C) the workpiece per surface area obtains total notes nitriding dosage D, is that computer reads workpiece total current, negative bias pulse width and the negative counting under each width with certain frequency, and is calculated as follows: $D=\frac{(1+\mathrm{\&eta;})}{e(1+\mathrm{\&gamma;})}(\underset{i}{\mathrm{\&Sigma;}}{I}_i\underset{j}{\overset{J\left(i\right)}{\mathrm{\&Sigma;}}}{\mathrm{\&tau;}}_{\mathrm{ij}}\&bull;n_{\mathrm{ij}})+\mathrm{\&alpha;T}$

D) in the nitridation process process, various parameter control are finished by computer, its program is to carry out multiparameter proportion integration differentiation PID according to the nitriding temperature curve of setting to control automatically, comparison by detected value in the computer and nitriding temperature curve or set(ting)value, and then adjustment bias pulse frequency, dutycycle and amplitude make actual nitriding temperature along nitriding temperature curve or set point change

E) processing step of the inventive method is:

The first step workpiece is prepared

Workpiece surface is cleaned, preferably be immersed in and use ultrasonic cleaning in the scavenging solution, airing then,

Second the step shove charge, vacuumize, inflated with nitrogen

With the workpiece of airing, be placed on the work piece platform in the main vacuum chamber, close door for vacuum chamber, be evacuated to 1 * 10 ^-2Pa～1 * 10 ^-4Behind the Pa, inflated with nitrogen makes air pressure reach 1Pa～1 * 10 again ^-2Pa,

The excitation of the 3rd step produces plasma body

Utilize direct current glow discharge, or radio frequency glow discharge, or microwave ECR discharge excitation generation plasma body around workpiece,

The 4th step started automatic nitriding sequence of control

Open positive negative pulse stuffing power supply and computer control system power supply, start automatic nitriding sequence of control, select or setting nitriding temperature curve, so computer, is adjusted control positive negative pulse stuffing parameter just by multiparameter proportion integration differentiation PID control principle, make actual nitriding temperature by the nitriding temperature curvilinear motion of setting, until end of processing, in case of unusual, system reports to the police automatically, and prompting is fixed a breakdown

The 5th step shut down, workpiece is come out of the stove detection

Behind the end of processing, auto stop, can take a sample and detect this moment, generally carries out conventional metallographic and Performance Detection.

2. the Plasma Source Ion Nitrided Processes and apparatus that computerizeds control according to claim 1 is characterized in that:

Positive negative pulse stuffing is produced by supervisory circuit being under computer control, and the right repetition rate of pulse is f, and its scope is 1KHz～20KHz, and positive pulse width is τ ₁, scope is , be generally 50 μ s～1ms, amplitude V ₁, scope is 500V～3000V, at insulation and temperature-fall period τ ₁=0, the width of negative pulse is τ ₂, scope is

, being generally 50 μ s～1ms, amplitude is V ₂, its scope is-500V～-3000V, and Δ t ₁=Δ t ₂=1 μ s is advisable.

3. the Plasma Source Ion Nitrided Processes and apparatus that computerizeds control, its equipment comprises main vacuum chamber [21], work piece platform [22], pumped vacuum systems [26], airing system [27], power supply system [28] and microwave source system [29], it is characterized in that: main vacuum chamber [21] is made of cylindrical housings, arranged outside at its housing has many little permanent-magnet blocks [20], the polarity of these small magnet pieces alternately changes according to certain rules arranges, constitute multipole cusp field structure, in main vacuum chamber [21] housing both sides, be provided with two electron cyclotron resonace ECR reaction chambers [18], they and UNICOM of main vacuum chamber [21], around ECR reaction chamber [18], be provided with ECR magneticfield coil [19], be provided with vacuum pump interface [24] in the main vacuum chamber bottom, the main vacuum chamber side is provided with hermatic door [23], automatically nitriding supervisory circuit [25] is joined by computer interface [13] and microcomputer [14], and microwave [15] is introduced ECR reaction chamber [18] by quartz window [17].

4. the Plasma Source Ion Nitrided Processes and apparatus that computerizeds control according to claim 3, it is characterized in that, by regulating magneticfield coil [19] electric current, make near the outlet of ECR reaction chamber and can produce and the corresponding resonant field intensity of microwave frequency, if adopting frequency is the microwave source of 2.45GHz, then producing the required magneticstrength of electron cyclotron resonace is 875 Gausses, permanent magnet [20] Surface field is 1500～2500 Gausses, be generally about 2000 Gausses, by the magnetism-free stainless steel locular wall, decay to 100～700 Gausses at the locular wall inner surface, be generally about 400 Gausses.

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