Process for determining the edge layer condition of objects.

Translation of description of equivalent WO 8810420 A2

p0001A method for detecting the surface layer state of bodies

p0002Description:

p0003The invention relates to a method for detecting the Rand¬schichtzustandes of bodies. Furthermore, the invention bereifft using this method.

p0004The nitriding as well nitrocarburizing stand alongside

p0005Carburizing currently the most important and most widespread method of thermochemical surface layer treatment. These are used to adjust the Eigenscnafte of components and work Zeugenen regard to wear, fatigue and corrosion resistance according to the demands placed on them. Despite the importance of these Verfahrer it has not yet managed to control Nxtrier- and nitrocarburizing sufficient accuracy and control. All previously used in practice inspection bodies for nitriding or nitrocarburizing in a gas stream are limited to the detection of the atmospheric conditions and the atmospheric condition in the treatment recipients during treatment. So in practice substantially NH₃Analyzers, as well as H₂-, CO, CO₂-, CH₄Analyzers for detecting the atmospheric condition for use. Chance also mass spectrometers to detect the composition of the atmosphere.

p0006By means of the determined from these measurements is set nitriding the desired composition of the atmosphere on the basis of experimentally determined teacher diagram by influencing the Gasdurehflüsse in the treatment recipients. However, there is no causal relationship between the composition of the atmosphere and the result of the surface layer treatment as other key predictors such as furnace state, batch size, material, and material surface condition, will not be considered.

p0007The processes mentioned have the disadvantage that they only control the composition of the atmosphere in the treatment recipient and provide no way to detect the edge shift state of a workpiece during the surface layer treatment.

p0008The invention therefore has the object of providing a process for "in situ" -Erfassung the boundary layer state.

p0009To achieve this object, the inventive method is characterized in that at least one electromagnetic size to the body during a treatment surface engineering is continuously measured. The inventive method offers the advantage that in contrast to the known methods, not a cause of the surface layer-treatment such as the atmosphere condition, is controlled, but the result of the surface layer treatment, namely, the current boundary layer condition is detected. By monitoring the actual state of the surface layer, a control of the surface layer treatment, in particular the atmospheric condition, for Erreiohun, a predetermined target state of the boundary layer is möglieh.

p0010In a thermochemlschen (boundary layer-IBehandlung measuring the electromagnetic size (n) depending on the material of the body and / or the particular type of treatment in one or more (test) Freguenzen done. This method is particularly useful in a surface layer treatment metallic materials by nitriding or mtrocarburieren.

p0011It measures the complex electromagnetic immittance, which provides information on the electric and magnetic state of the material, üur limit the effort involved in carrying out the method is the measurement of a material sample of the same material, material condition and material boundary layer condition as the rest, the boundary layer undergoing treatment charging made.

p0012The method also offers the possibility of the immittance of a combination of the body (sample) to measure with electrical devices or instead to refer to the immittance of the body, the detuning of a resonant circuit, which includes the body, of the current Randschiohtzustandes.

p0013The measured Immitanzwerte permit based on calibration curves direct Rückechluß on the surface layer state characteristic variables, such as the hardening depth, the diffusion depth and the compound layer thickness.

p0014By cooling or heating of the body (sample), the temperature-dependent immittance complex can be determined. This leads via the determination of Phasenumwandungstemperatur (eg, Curie temperatures) for determining the phase composition in the connection layer and in the (underlying) layer diffusion of the measured Randsehiehtbereiches. Depending on the setting of the (test) frequency, the measurement can be limited to a particular layer of the boundary layer region.

p0015The size of the Immitanzanderung the Curie point of a phase is a quantitative measure for that phase. For composite phases with concentration-dependent Curie points, especially in the ferromagnetic phase Fe₄N, Fe₄ (C, N), Fe_2-3N, Fe_2-3(C, N), measuring the Immitanzanderung for determining the concentration of carbon and nitrogen is used.

p0016The thickness of the composed of ferromagnetic phases compound layer is therefore determined from the sum of the Immitanzänderungen in the Curie points.

p0017The inventive method thus enables control of the surface layer treatment to targets as Verbindungsschiehtdicke, hardening depth, tie layer composition and nitriding, in conjunction with the atmosphere control in the treatment recipients of fully automatic control and regulation of Randsehicht treatment to achieve a predetermined boundary layer state is feasible.

p0018The invention will be explained in more detail with reference to the drawings. Therein:

p0019FIG. 1 shows a typical resistance curve with a measuring frequency of 10 kHz,

p0020Fig. 2 shows the relationship between Phasenzusaramensetzung or connecting layer thickness and relative resistivity at a measuring frequency of 10 kHz,

p0021Fig. 3 shows a cooling curve showing the temperature-dependent inductance,

p0022Fig. 4 shows a further cooling curve with the dependencies shown in FIG. 3,

p0023FIG. 5 shows the dependency of the Curie point of the Fe_2-3N- phase of the nitrogen concentration, and

p0024Fig. 6 shows the dependence of the Curie point of the Fe_2-3CN phase of the nitrogen and carbon concentration.

p0025The detection of the boundary layer state of bodies (samples of material) by means of measurement of electromagnetic parameters for a surface layer treatment, such as nitriding or nitrocarburizing, the treatment recipient. Accordingly done according to the invention to measure "in situ".

p0026Is in this case measured with an alternating current signal (AC). In this way, the well-known of the metrology her "skin effect" to be exploited, which manifests itself in the fact that limited an electromagnetic current to a diminishing marginal area with increasing frequency. Thus, can be varied by adjusting a frequency corresponding to the to be measured edge region so that electric and magnetic properties of samples can be selectively determined to very thin surface layer areas (microns). The skin effect also has the consequence that the Verringeruunng a current-carrying cross-section samples the measurement signal is increased, and thus a much greater detection sensitivity than in the case of the DC current measurement is achieved.

p0027Mathematically, describes the combination of an electrical conductor as a network system. this one uses so-called two poles, such as resistors R, capacitors C and inductors L, but no power-generating conductor, it is called linear, passive network elements.

p0028When an alternating voltage U applied to a linear, passive network system, a current flows I. In complex notation, the two variables can be represented as follows;

p0029U = U_O · e^jwt

p0030I = I_O · e^{j (wt-θ)}

p0031U: complex ac

p0032U_O : RMS voltage

p0033I: complex AC

p0034I_O: RMS current w: angular frequency (w = 2 / if) θ: phase angle t: time

p0035From the ear ashes law the complex AC impedance, the impedance Z is calculated, depending on the frequency as the quotient of two quantities:

p0036Z (w) = V / I = <img id="imgf000008_0001" he="25" wi="40" file="imgf000008_0001.tif" img-format="tif" img-content="drawing" orientation="portrait" inline="no" />

p0037Z (w) = / Z / · e^{j θ} Analogous to the impedance is the Wechselstromleitwert, the admittance Y are defined. The following applies:

p0038Z (w) = 1 / Y (w)

p0039Impedance and admittance are summarized under the term immittance.

p0040In general, the voltage, the current and the phase angle are measured and from these values, all other variables are calculated result.

p0041The measuring device used for performing the method consists essentially of a Immitanzmeßgerät, commercially referred to inter alia as LCR-current-measuring device, a sensor with interchangeable measuring sample and a (shielded) electric line between the present in the treatment recipients probe and the Immitanzmeßgerat with appropriate adaptation to the probe.

p0042The probe consists of a temperature-stable, chemically resistant, electrically conducting in the treatment recipient with a temperature-stable, chemically resistant electrically insulating the Meßzuleitungen (AI₂ O₃, Mica), the Meßzuleitungen with a shield (Ti (C, N) coated sheathing or contacts) is provided to Meßverfälschungen as the drift of the measurement signal to avoid, and an electromagnetic (inductive) coupling of the leads to the sample ,

p0043In the nitration (32 h) a sample of material from 31CrMoV9 at 520 ° C and a nitriding of k_n = 0.4 arise in carrying out the method using the measuring apparatus described at the outset in the following with reference to Figs. 1 to 6 explained in more detail values. In Fig. 1, a typical resistance characteristic at 10 kHz measurement frequency, from the Immitanzmessung is determined, applied during the entire nitriding operation including heating and cooling. Here one can see the typical exponential decay of the measured values ​​as a function of nitriding, as is to be expected with all diffusion-controlled processes.

p0044In FIG. 2 three measurements on three completely the same sample output states during identical nitriding treatments are presented. As accompanying investigations showed, it is in Samples 11 and 12 both with respect to the layer composition and the thickness of the connection and diffusion layer to layer identical edge states. In contrast, sample 13 shows how even reflected slight differences in phase composition and thickness of the compound layer in Meß.signal. One can see how sensitive the measurement signal reflects the true state of nitriding.

p0045Fig. 3 shows a Abkühlmessung. Shown is the inductance curve of the sample, determined from the Immitanzmessung, depending on the temperature. The measurement frequency is 1 MHz. This cooling curve recorded at the end of the nitriding treatment of FIG. 2 with the specimen 11. It is identical with the history of the sample 12. At 482 ° C clearly shows the Curie point of the Fe₄N-phase because the inductance despite falling temperature suddenly rises or at low levels of this phase at least one breakpoint. The curve is parallel offset. The size of the parallel shift is proportional to the phase portion in measured volume and can thus be used by means of a calibration for quantitative phase determination.

p0046FIG. 4 shows the concentration determination by the determination of the Curie temperature (s). The Ab shown künlkurvenverlauf A was added nitriding treatment of the sample 13 of the end (shown in Fig. 2). The measurement frequency is 1 MHz. Here one recognizes another curie point at 345 ° C in addition to the at 462 ° C.

p0047In Fig. 5 is the dependence of the Curie point of the Fe_2-3N phase represented by the nitrogen concentration. Fig. Figure 6 shows the dependence of the Curie point of the Fe_2-3CN-Phile of nitrogen + Kohlenstoffkonzentratlon. The assignment is here an additional ε-Eisencarbonitridphase with the concentration of 5.5 wt.%.

p0048One possible use of the method described is of Dia also for other boundary layer treatments, such as TVD (Physical Vapor Deposition ,, CVD IChemical Vapor Deposition) I to PACVD (Plasma Assisted Chemical Vapor Deposition), as well as for general use with respect to ceramics and plastics , debkbar. The application in the Community dueses method is also not limited to the time during a surface layer treatment, but also enables detection dxe desRandschichtzustandes on subsequent cooling. This circumstance allows the Durchhführung of analyzes of the boundary layer region irrespective of a surface layer treatment.