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

Abstract

In the field of material surface modification, the plasma source ion nitriding process and equipment controlled by computer, including heating, heat preservation, cooling and ion injection permeation process and power supply system, gas supply system, vacuum system and main vacuum chamber The equipment is characterized by the use of self-heating to heat the workpiece, and the computer automatically controls the repetition frequency of positive and negative pulse pairs, their respective duty ratios and amplitudes to control the temperature of the workpiece, so that it can be controlled according to the set nitriding temperature curve. Changes, advantages: simplified equipment, reduced energy consumption by 40%, fully automated process, stable process, no sparking, no arcing, no annealing of the workpiece, safe and reliable, and good repeatability.

Description

Plasma Source Ion Nitriding Process and Equipment Controlled by Computer

The invention relates to an ion nitriding process and belongs to the technical field of material surface modification.

The nitriding process is an important means of material surface strengthening. At present, the most advanced nitriding process is the plasma source ion nitriding process. This process usually includes the following three contents: ① Place the workpiece to be nitrided in a vacuum chamber After vacuuming, it is filled with low-pressure nitrogen, and then a nitrogen plasma is generated by a certain discharge mechanism; ②Start the heater placed next to the workpiece to heat the workpiece, and adjust the power of the heater to control the temperature of the workpiece; ③For A DC or pulse negative bias is applied to the workpiece to attract positive ions in the nitrogen plasma to infiltrate the surface of the workpiece. In the prior art, there are two main problems in the process of realizing this process: ① using a side-heating heater to heat the workpiece, which not only makes it difficult to heat evenly for workpieces with complex shapes, but also increases the number of heaters. It reduces the complexity of the system, and forms certain interference and pollution to the plasma space; ②Plasma source ion nitriding process is a multi-parameter control process, these parameters include: plasma density, plasma electron energy distribution function, working Gas pressure, workpiece bias parameters, nitrogen ion flux density, nitriding temperature, nitriding time and total nitriding dose, etc. The adjustment of these parameters is done manually in the prior art. This manual adjustment method is very random, changes at any time, and varies from person to person. Therefore, it is difficult to guarantee the repeatability of the process, and it requires the operator to concentrate on monitoring at any time, which increases the labor intensity.

Purpose and task of the present invention are to overcome prior art in nitriding process, 1. need the side heating type heater and the system complexity that brings thereby and to the disturbance, pollution that plasma space forms; 2. to plasma source The multi-parameter process of the ion nitriding process needs manual monitoring, and the lack of automatic control cannot be realized. A method of self-heating the workpiece without installing a heater is proposed. At the same time, a computer is used to automatically monitor the process, so that the plasma source ion Nitriding has become a fully automated process, and the technical solution of the present invention is specially proposed.

In the nitriding process, the workpiece needs to be added with a series of negative bias pulses. The negative pulses attract positive nitrogen ions to infiltrate the surface of the workpiece. It is converted into heat energy to increase the temperature of the workpiece. If the heat generated during ion bombardment is equal to the heat lost due to thermal radiation, the workpiece can be maintained at a certain temperature. Obviously, the ion bombardment brought to the workpiece per unit time Thermal energy is related to pulse frequency, pulse amplitude and duty cycle.

In order to further clarify this relationship and realize the purpose of fully automatic control, the principle of self-heating is firstly explained. When the workpiece "soaked" in the plasma to be nitrided is applied with pulse negative bias, a sheath layer is formed on its surface. According to the theory of molecular kinematics, the number of ions hitting the surface of the sheath layer per unit area per unit time is : $\frac{1}{4}{\mathrm{no}}_i{\stackrel{\‾}{v}}_i$

Where ni is the ion density, vi is the average velocity of ion thermal movement, under the condition of negative bias, these positive ions can pass through the sheath and reach the surface of the workpiece, so the ion current density j _i entering the surface of the workpiece is $j_i=\frac{1}{4}{\mathrm{en}}_i{\stackrel{\‾}{v}}_i=\frac{1}{4}{\mathrm{en}}_i{({\mathrm{kT}}_i/m_i)}^{\frac{1}{2}}$

Where e is the unit charge, kT _i is the ion temperature, and m _i is the ion mass.

Since the time to establish a sheath is generally less than 1 μs, which is much shorter than the width of the negative pulse, the change of the ion current density during the formation of the sheath can be ignored, and it is considered that the ion current density during the negative pulse is j _i .

Assuming that the negative pulse frequency is f and the pulse width is τ ₂ , then the average ion current density j _i is:

Assuming that the pulse negative bias voltage amplitude is V ₂ , the power density p _i generated by ion bombardment on the workpiece surface is: $p_i={\stackrel{\‾}{j}}_i\&Center\; Dot;V_2=\frac{1}{4}{\mathrm{en}}_i{\mathrm{f\τ}}_2{V}_2{({\mathrm{kT}}_i/m_i)}^{\frac{1}{2}}$

Assuming that the surface area of the workpiece exposed to the plasma is S, the power _Pi generated by ion bombardment is: $P_i={\stackrel{\‾}{j}}_i{V}_2\&Center\; Dot;S=\frac{1}{4}{\mathrm{en}}_i{\mathrm{f\τ}}_{2}S{({\mathrm{kT}}_i/m_i)}^{\frac{1}{2}}$

Obviously, for a certain workpiece, that is, S is constant, and under certain plasma parameter conditions, that is, ni _, kT _i , mi _are constant, and the repetition frequency f, pulse width τ ₂ and amplitude V ₂ of the negative pulse are adjusted, The total power injected into the workpiece can be controlled.

When a positive pulse is applied to the workpiece, it will cause electrons to bombard the workpiece, and the pulse electron current density j _e can be calculated as follows: $j_e=\frac{1}{4}{\mathrm{en}}_e{\stackrel{\‾}{v}}_e$

Among them, n _e is the electron density, and _ve is the average velocity of electron thermal motion. Similar to the case of negative pulse, the formulas of average electron current density j _e , electron heating power density pe _and total electron heating power P _e can be derived : ${\stackrel{\‾}{j}}_e=\frac{1}{4}{\mathrm{en}}_e{\mathrm{f\τ}}_l{\left({\mathrm{kT}}_e\right)}^{\frac{1}{2}}$ $p_e=\frac{1}{4}{\mathrm{en}}_e{\mathrm{f\τ}}_l{V}_l{\left({\mathrm{kT}}_e\right)}^{\frac{1}{2}}$ $p_e=\frac{1}{4}{\mathrm{en}}_e{\mathrm{f\τ}}_l{V}_{l}S{\left({\mathrm{kT}}_e\right)}^{\frac{1}{2}}$

where τ ₁ is the positive pulse width, V ₁ is the positive pulse amplitude, and kT _e is the electron temperature

Since v _e ＞＞ vi

Therefore j _e ＞＞j _i

That is, the positive pulse has a much larger heating power than the negative pulse, generally about two orders of magnitude larger, which is particularly meaningful for the heating up stage of large workpieces.

It can be seen that, in the heating stage, heat preservation stage and cooling stage of the actual operation, the ion bombardment power and the electron bombardment power are adjusted to satisfy:

① Heating stage:

②Insulation stage:

Ion bombardment power = power loss caused by heat radiation, etc.

③Cooling stage:

It is not difficult to see that if the ion bombardment power<the power loss caused by thermal radiation, etc., then the system is in the cooling stage.

Obviously,

is the natural cooling rate to stop ion bombardment.

Therefore, throughout the nitriding process, the temperature of the workpiece can be controlled by adjusting the repetition frequency, pulse width and amplitude of the positive and negative pulses. This is the basic principle of computer-controlled nitriding process.

For smaller workpieces, the three stages of nitriding can achieve temperature control by adjusting the negative bias pulse parameters; however, for large workpieces, due to their large heat capacity, in the heating stage, only ion bombardment , Sometimes the required heating rate cannot be reached, so electron bombardment is also used to increase the heating rate of the workpiece. This is achieved by employing positive and negative bias pulse pairs.

The basic idea of the present invention is to remove the side-heating heater, adopt the self-heating heating workpiece of ion/electron bombardment workpiece, adopt positive and negative bias voltage pulse pairs, and control their repetition frequency and their respective duty ratios and amplitudes. The temperature changes along the set nitriding temperature curve, the computer is used to detect the temperature of the workpiece, and the detected value is compared with the set value in the computer, so that the detected value tends to the set value or swings around the set value, and the control Wen software adopts multi-parameter proportional-integral-differential PID control technology. The total nitriding dose obtained per unit surface area of the workpiece is obtained by reading the total current of the workpiece, the negative bias pulse width and the pulse width of each width through the computer at a certain frequency. Negative pulses are counted and calculated according to the given equation. For the sake of safety, arc current discrimination system and feedback control circuit are also set up in the system.

The computer-controlled plasma source ion nitriding process and equipment proposed by the present invention include a set temperature rise, heat preservation and temperature drop process and ion infiltration process. It is characterized in that: the workpiece is heated by self-heating, that is, using The energy of the ion/electron bombardment workpiece heats the workpiece; the temperature control of the workpiece heating, heat preservation and cooling process is to adjust the temperature of the workpiece by adjusting the frequency, amplitude and duty cycle of the negative bias voltage of the workpiece. For large workpieces, the required The temperature rise rate is also used for electron bombardment. At this time, it should be realized by using positive and negative bias pulse pairs. The positive and negative pulse pairs have the same repetition frequency, and their occurrence times are completely staggered and have a certain time interval. The value and duty cycle can be adjusted independently. When adjusting, the positive and negative pulses should meet the following relationship with the repetition frequency T: $T=\frac{1}{f}={\mathrm{\&tau;}}_1+{\mathrm{\&tau;}}_2+\mathrm{\&tau;}+\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="A9910156800141.png"\; state="\{\{state\}\}">t</figure-callout>}}_1+\mathrm{\&Delta;}{t}_2$ Where τ ₁ is the positive pulse width, τ ₂ is the negative pulse width, τ is the time that τ ₁ and τ ₂ can take up, Δt ₁ is the interval between positive pulse and negative pulse, Δt ₂ is the minimum interval between negative pulse and positive pulse , by adjusting the repetition frequency of the positive and negative pulse pairs and their respective duty ratios and amplitudes, the temperature of the workpiece can be changed within a certain error range along the set nitriding temperature curve. The amplitude of the positive pulse in each stage is taken as zero; the total nitriding dose D obtained per unit surface area of the workpiece is obtained by the computer reading the total current of the workpiece, the negative bias pulse width and the negative pulse at each width at a certain frequency. Count and calculate as follows: $\mathrm{D.}=\frac{(1+\mathrm{\&eta;})}{e(1+\mathrm{\&gamma;})}(\underset{i}{\mathrm{\&Sigma;}}{I}_i\underset{j}{\overset{J\left(i\right)}{\mathrm{\&Sigma;}}}{\mathrm{\&tau;}}_{\mathrm{ij}}\&bull;{\mathrm{no}}_{\mathrm{ij}})+\mathrm{\&alpha;}{T}_0$ Among them, η is the proportion of nitrogen molecular ions in the nitrogen plasma, e is the electronic charge; γ is the target material, that is, the secondary electron emission coefficient of the workpiece, I _i is the i-th value of the total current of the workpiece, and τ _ij is the In the case of the same I _i , the jth negative bias pulse width value, n _ij is the count of negative bias pulses under the negative bias pulse width value τ _ij , and α is the certain value of the injection nitriding when the workpiece is not biased. The proportional constant of the contribution, T ₀ is the total time for the workpiece to be unbiased, and can usually be calculated as follows: $T_0=\underset{k}{\mathrm{\&Sigma;}}{\mathrm{no}}_k({\mathrm{\&tau;}}_k+\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="A9910156800141.png"\; state="\{\{state\}\}">t</figure-callout>}}_1+\mathrm{\&Delta;}{t}_2)$ Among them, τ _k is the kth value of τ, n _k is the number of τ _k taken by τ; during the nitriding process, the workpiece temperature is cyclically detected, the positive and negative pulse parameters are controlled, and the nitriding dose is calculated. All are completed by computer. The temperature control software adopts multi-parameter proportional integral differential PID control technology. By comparing the detected value in the computer with the nitriding temperature curve or set value, the bias pulse frequency, duty cycle and amplitude are adjusted to make the detection Value tends towards set value, or swings near set value; Process step of the present invention is:

The first step workpiece preparation

Clean the workpiece to be nitrided, usually by immersing it in the cleaning solution, cleaning it with ultrasonic waves, and then drying it;

The second step is to load the furnace, vacuumize and fill with nitrogen

Place the dry workpiece on the workpiece platform in the main vacuum chamber, close the vacuum chamber, and evacuate to 1×10 ^-2 Pa ~ 1×10 ^-4 Pa, generally 2×10 ^-3 Pa, and then pass the mass The flowmeter injects nitrogen gas into the vacuum chamber to make the air pressure in the vacuum chamber reach 1Pa～1×10 ^-2 Pa, generally 8×10 ^-2 Pa;

The third step stimulates the generation of plasma

Turn on the power, use DC glow discharge, or radio frequency glow discharge, or microwave ECR discharge to excite and generate plasma around the workpiece;

The fourth step starts the automatic nitriding control program

Turn on the positive and negative pulse power supply and the computer control system power supply, start the automatic nitriding control program, select or set the nitriding temperature curve, then, the computer adjusts the positive and negative pulse parameters according to the multi-parameter proportional integral differential PID control principle, so that the actual The nitriding temperature changes along the nitriding temperature curve until the end of the process. In case of abnormality, the system will automatically alarm and prompt to eliminate the fault;

The fifth step is shutdown, sampling, quality and performance inspection

After the process is over, it will stop automatically, and samples can be taken and tested at this time, usually for routine metallographic and performance testing.

-Δt₂，一般为50μs～1ms，幅值V₁，其范围为500V～3000V，在保温阶段与降温阶段τ₁＝0，即无正脉冲。负脉冲镀为τ₂，其范围为 ，一般为50μs～1ms，幅度为V₂，其范围为-500V～3000V，而Δt₁＝Δt₂＝1μs为宜。The process of the present invention is further characterized in that the positive and negative pulse pairs are generated by a monitoring circuit under the control of a computer, the repetition frequency of the pulse pair is f, and its range is 1 kHz to 20 kHz, and the positive pulse width is τ ₁ , and its range for

-Δt ₂ is generally 50μs~1ms, the amplitude V ₁ is in the range of 500V~3000V, and τ ₁ =0 in the heat preservation stage and the temperature drop stage, that is, there is no positive pulse. Negative pulse plating is τ ₂ , and its range is , generally 50μs~1ms, the amplitude is V ₂ , the range is -500V~3000V, and Δt ₁ =Δt ₂ =1μs is appropriate.

Generally speaking, the selection of frequency is related to the shape of the workpiece to be nitrided. For workpieces with edges and corners, a higher frequency should be selected to avoid arcing; the energy deposition mainly depends on the pulse amplitude and duty cycle. Therefore, in the heating stage, V ₁ , V ₂ , τ ₁ , and τ ₂ take larger or maximum values; in the heat preservation stage and cooling stage, τ ₁ = 0, that is, there is no positive pulse, and V ₂ and τ ₂ take smaller values value or minimum value.

In order to realize the technical scheme of the plasma source ion nitriding process and equipment controlled by computer proposed by the present invention, the equipment adopted includes main vacuum chamber [21], workpiece platform [22], vacuum pumping system [26], supply Gas system [27], power supply system [28] and microwave source system [29] are characterized in that: the main vacuum chamber [21] is made of a cylindrical shell, and many small permanent Magnets[20], the polarities of these magnets are arranged alternately according to certain rules, forming a multi-pole tangential field structure, which acts as a magnetic confinement for the plasma. In order to increase the plasma density in the vacuum chamber and improve its uniformity, the On both sides of the shell of the main vacuum chamber [21], there are two electron cyclotron resonance ECR reaction chambers [18], which communicate with the main vacuum chamber. Around the ECR reaction chamber, there are ECR magnetic field coils [19]. A vacuum pump interface [24] is provided at the bottom of the vacuum chamber, and a sealed door [23] is provided on the side of the main vacuum chamber, where workpieces can be taken and placed. The automatic nitriding monitoring circuit [25] is connected with the microcomputer [14] through the computer interface circuit [13] , the microwave [15] is introduced into the ECR reaction chamber [18] through the quartz window [17] which acts as a seal.

The further feature of the device of the present invention is: by adjusting the current of the electromagnetic coil [19], the resonant magnetic field intensity corresponding to the microwave frequency can be generated near the outlet of the ECR reaction chamber. The magnetic strength of the permanent magnet is 875 gauss, and the surface magnetic field strength of the permanent magnet is 1500-2500 gauss, generally about 2000 gauss. Around 400 Gauss.

Corresponding to different microwave frequencies, different resonant magnetic field strengths are required. If the microwave frequency is fixed, the resonant magnetic field strength is also fixed. Similarly, the surface magnetic field strength of the permanent magnet block is also fixed, therefore, after passing through a certain non-magnetic stainless steel chamber wall, it will also decay to a certain magnetic field strength inside the chamber wall. When the microwave [15] with a frequency of 2.45 GHz is introduced into the ECR reaction chamber [18] through the quartz window [17], high-density nitrogen plasma can be generated by electron cyclotron resonance excitation at 875 Gauss. The body can fill the entire main vacuum chamber. At this time, the positive/negative pulse bias voltage generated by the monitoring circuit [25] is applied to the workpiece [1], and the nitriding treatment can be started. During the nitriding process, the computer software automatically Adjust the frequency f of the positive and negative pulse pairs, their respective amplitudes V ₁ , V ₂ and pulse width τ ₁ , τ ₂ , so that the temperature of the workpiece changes along the set nitriding temperature curve within a certain error range, thus, completely The nitriding process is completed automatically.

The main advantages of the technical scheme of the computer-controlled plasma source ion nitriding process and equipment proposed by the present invention are: 1. Since the equipment removes the heater and adopts a self-heating mode, not only the equipment is simplified, but also the workpiece is improved. The surrounding plasma state makes the heating uniform and the effect is better; ②In the computer-controlled nitriding process, the computer program performs multi-parameter proportional integral differential PID control according to the set temperature curve, with fast feedback response and high control precision, which is An automated and repeatable process, especially suitable for industrial application; ③ Since the computer can record in detail the actual temperature of the workpiece, the total current of the workpiece, the change history of the frequency, amplitude and duty cycle of positive and negative pulse pairs, so , the computer can give the total infiltration dose of the workpiece and the change curve of the total current of the workpiece, which provides reliable data for evaluating the nitriding effect; ④Computer-controlled nitriding process, no sparking, no arcing, and no Annealing is a safe process operation method; ⑤Because the heater is removed, the power consumption can be saved by about 40%.

The following is a description of the accompanying drawings

Fig. 1 is the schematic diagram of the structure of the positive and negative pulse pairs added to the workpiece in the present invention

Under the control of the computer, the positive and negative pulse pairs generated by the monitoring circuit have the same repetition frequency. The positive and negative pulses are completely staggered in time, and there is a certain time interval between them. The width of the positive pulse is τ ₁ , The amplitude is V ₁ , and τ ₁ =0 is taken during the heat preservation and cooling stages, that is, there is no positive pulse. The width of the negative pulse is τ ₂ , the amplitude is V ₂ , and τ is the adjustment margin of τ ₁ and τ ₂ , that is, the time that τ ₁ and τ ₂ can take up. When adjusting, the repetition frequency T of positive and negative pulse pairs 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 a structural schematic diagram of the present invention for automatic nitriding monitoring circuit [25]. The part inside the dashed box is the monitoring circuit[25]

On the one hand, the function of this circuit is to monitor the temperature of the workpiece and other operating parameters at any time, and on the other hand, it receives the control signal of the computer, and realizes the control of the temperature of the workpiece through the adjustment of the frequency, pulse width and pulse amplitude of the positive and negative pulse pairs. control.

The thermocouple attached to the workpiece [1] to be nitrided sends the temperature signal to the isolation amplifier [2]. The function of the isolation amplifier is to isolate the bias voltage on the workpiece so that it cannot be transmitted to the computer interface [ 13] circuit, but the temperature signal can only be transmitted to the computer interface [13]. The computer controls the negative pulse by sending three digital-to-analog conversion D/A signals through the computer interface [13] to control the frequency f, Pulse width τ ₂ and pulse amplitude a ₂ , [4] is a voltage-frequency conversion VFC circuit, and [5] is a delay circuit, so that the negative pulse is generated after a delay of time Δt ₁ after the end of the positive pulse, so as to ensure the system Stable work, [6] is the voltage pulse width conversion circuit, [7] is the drive circuit, it amplifies the power of the pulse signal whose frequency and pulse width have been adjusted, so as to drive the pulse modulator IGBT[8], [9 ] is a digitally controlled DC power supply, whose output amplitude is controlled by the D/A signal _a2 of the computer. After the DC output of the digitally controlled DC power supply [9] is modulated by the IGBT [8], it outputs a high-power pulse signal to the pulse transformer [ 3] a set of input coils, and a negative pulse is induced in the output coil and applied to the workpiece [1]. The generation of the positive pulse is completely similar to the negative pulse, and the difference in polarity is achieved by the different coupling phases of the primary and secondary coils of the pulse transformer [3]. The current sensor [12] can measure the workpiece ion current _I2 and the electronic current _I1 and send it into the computer through the computer interface [13]. The output of the current sensor [12] is also sent to the comparator [11] at the same time. If the workpiece current is greater than At a certain critical value, the comparator [11] will have a signal output to the feedback control circuit [10] to realize the protective control of the digitally controlled DC power supply [9]. Voltage pulse width conversion circuit [6], the output pulses are not only sent to the drive circuit [7], but also sent to the computer interface [13] for pulse counting, namely n ₁ and n ₂ , so as to realize the monitoring function.

Fig. 3 is the structural representation of the plasma source ion nitriding equipment designed by the present invention with computer control

There are many small pieces of permanent magnets [20] placed on the outside of the cylindrical main vacuum chamber [21] made of stainless steel, and their polarities are arranged alternately according to certain rules, forming a multi-pole tangential field structure, which plays a role in the indoor plasma. Constraint effect, the mechanical pump and molecular pump system connected to the pumping port [24] communicate with the main vacuum chamber, a nitrogen inlet [16] is provided at the end of the ECR reaction chamber [18], and a gas mass The flow meter is used to adjust the intake rate. On both sides of the main vacuum chamber [21], there are two electron cyclotron resonance ECR reaction chambers [18] with quartz windows [17], communicating with the main vacuum chamber [21]. , the ECR magnetic field coil [19] is set outside the electron cyclotron resonance ECR reactor [18]. By adjusting the coil current, an 875 Gauss magnetic field can be generated at the exit of the ECR reaction chamber [18]. Microwaves with a frequency of 2.45 GHz [15] are introduced into the ECR reaction chamber through the quartz window [17] which acts as a seal, and high-density nitrogen plasma can be excited by electron cyclotron resonance at 875 Gauss. Due to the diffusion effect, the plasma Body just can be filled with whole main vacuum chamber, at this moment, the positive/negative pulse bias voltage that monitoring circuit [25] produces is added on the workpiece [1]. Just can start nitriding treatment, workpiece [1] is to be placed on workpiece platform [22], and workpiece platform [22] is connected with computer [14] by monitoring circuit [25] and computer interface circuit [13], computer software automatically Adjust the frequency of positive and negative pulse pairs, as well as their respective amplitude and pulse width, so that the temperature of the workpiece changes along the set nitriding temperature curve within a certain error range, so that the nitriding process can be completed automatically. Symbol [23] is the airtight door of the main vacuum chamber. Inside the dotted box is the main vacuum chamber system [30]. The direction of the arrow indicated by the symbol [15] in the figure is the direction of microwave entrance; the direction of the arrow indicated by the symbol [16] is the direction of nitrogen gas inlet; the direction of the arrow indicated by the symbol [24] is the direction of gas extraction.

Fig. 4 is the schematic diagram of the plasma source ion nitriding equipment system designed by the present invention, the main vacuum chamber system [30] is equipped with power supply system [28], gas supply system [27], vacuum pumping system [26] And the microwave source system [29], the computer [14] is connected with the monitoring circuit [25] through the computer interface circuit [13], so as to automatically monitor the nitriding process.

这里T₀表示室温。无疑，也可设定其他形成的氮化曲线。接着氮化开始，激励产生氮等离子体，时间清零；在升温阶段，循环检测工件实际温度T_m(t)，并将它与T_c(t)比较，根据二者的差值，进行多参数PID调节，即调节正负脉冲对的频率及各自的宽度与幅度，使差值减小，直到T_m(t)≥T_H，即达到T_c(t)在保温阶段的取值，此时转入保温阶段；在保温阶段，依旧循环检测工件的实际温度T_m(t)，并将它与T_c(t)比较，根据二者的差值进行多参数PID调节，使差值减小；对负脉冲期间的工件总电流进行跟踪记录，对每一种工件总电流下的负脉冲宽度，以及每一种负脉冲宽度下的脉冲计数进行记录，同时也对τ值进行跟踪记录，计算机根据这些数值利用前述公式计算工件所接收的氮化剂量D(t)，直至D(t)≥D₀，即达到预期的氮化剂量，此时转入降温阶段，时间重新置零；在降温阶段，依旧循环检测工件的实际温度T_m(t)，并将它与T_c(t)比较，根据二者的差值进行多参数PID调节，使差值减小，直至T_m(t)≤T，氮化结束。Fig. 5 is a computer automatic control program flow chart of the process of the present invention, and the arrow in the figure is the progress direction of the flow process. After the automatic nitriding program starts, first set the heating rate a, maintain the temperature T _H , the dose required for nitriding D ₀ , the cooling rate b and the end temperature T; therefore, the nitriding temperature curve T _c (t) can be expressed as

Here T ₀ means room temperature. Of course, other formed nitriding curves can also be set. Then nitriding starts, the nitrogen plasma is stimulated, and the time is reset; in the heating stage, the actual temperature T _m (t) of the workpiece is cyclically detected, and it is compared with T _c (t). According to the difference between the two, multiple Parameter PID adjustment, that is, to adjust the frequency of positive and negative pulse pairs and their respective width and amplitude, so as to reduce the difference until T _m (t) ≥ T _H , that is, to reach the value of T _c (t) in the heat preservation stage. In the heat preservation stage, the actual temperature T _m (t) of the workpiece is still cyclically detected, and compared with T _c (t), and the multi-parameter PID adjustment is performed according to the difference between the two to reduce the difference. Small; track and record the total workpiece current during the negative pulse period, record the negative pulse width under each kind of total workpiece current, and the pulse count under each negative pulse width, and also track and record the τ value, Based on these values, the computer calculates the nitriding dose D(t) received by the workpiece using the aforementioned formula until D(t)≥D ₀ , that is, the expected nitriding dose is reached. At this time, it enters the cooling stage, and the time is reset to zero; In the cooling stage, the actual temperature T _m (t) of the workpiece is still cyclically detected, and compared with T _c (t), and multi-parameter PID adjustment is performed according to the difference between the two to reduce the difference until T _m (t )≤T, nitriding ends.

The details of the present invention will be further described below in conjunction with specific embodiments.

A Cr18Ni9Ti stainless steel rotating shaft used on a piston ring cleaning machine, with a size of 35 × 280 millimeters, requires surface wear resistance and corrosion resistance, and adopts the technology of the present invention to carry out nitriding treatment. The steps are as follows:

The first step workpiece cleaning

Put the workpiece into the ultrasonic cleaning machine, add cleaning solution, turn on the ultrasonic wave, and clean it for 15 minutes. After taking it out, scrub it with acetone cotton, then wipe it with anhydrous alcohol cotton, and finally dry it in the air.

The second step is to load the workpiece and vacuumize

Put the workpiece into the workpiece platform in the main vacuum chamber of the computer-controlled plasma source ion nitriding equipment of the present invention, close the vacuum chamber door, and turn on the mechanical pump and the molecular pump in succession to make the background vacuum of the vacuum chamber reach 2×10 ^-3 Pa.

Step 3: Microwave ECR excites nitrogen plasma

Fill the vacuum chamber with nitrogen gas through the mass flowmeter to make the pressure reach 8×10 ^-2 Pa; at this time, turn on the power supply of the magnetic field coil and adjust the coil current to generate a magnetic field of 875 gauss at the outlet of the ECR reaction chamber; then turn on the frequency of 2.45GHz microwave source, adjust its power output to 630 watts. At this time, the light purple glow from the ECR reaction chamber and the main vacuum chamber shows that the nitrogen plasma has filled the main vacuum chamber. The plasma density was measured with a Langmuir probe to be 2.3×10 ¹⁰ /cm ³ , and the electron temperature was 6.2 eV.

The fourth step starts the automatic nitriding program

Turn on the power supply of the monitoring circuit and the positive and negative DC power supply, and after starting the automatic nitriding program, the screen will display the parameter setting interface. Here, set the heating rate a=1°C/s, the cooling rate b=0.2°C/s, the temperature in the holding stage T _H =400°C, the amount of nitriding D ₀ =4×10 ²¹ /cm ² , and the end temperature T=60 ℃, after clicking “Confirm” with the mouse, the program will enter the heating stage, and it will transfer to the heat preservation stage after about 6 minutes. After the heat preservation stage lasts for 4 hours, it will automatically transfer to the cooling stage. .

Step Five Quality Check

A nitride layer with a thickness of about 6 μm was formed on the surface of the metallographic examination.

Microhardness check, surface hardness was 724HV under 25g load.

Small angle X-ray diffraction analysis observed five γ _N peaks from the supersaturated nitrogen austenite phase of the nitrided layer.

The electrochemical corrosion test shows that after about 4 hours of nitriding treatment, the surface corrosion resistance has not changed.

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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