Influence of the parameters of hydrogen nitrogen nitrogen in a glow discharge on tribological and physico

Fig. 2 Diffraction patterns and microsections of 40X steel samples: a - nitriding according to mode 7; b - according to mode 5; c - according to mode 9

Table 3

Thickness of nitride hN, diffusion layers h and surface microhardness HV0.1

Fig. 5 Dependences of the depths of the diffusion sphere h (a) and the nitride zone (b) on the voltage value U; also (c, d) on the value of the current density j (I and II are different forms of suspensions) with the interdependent characteristics of the BATR

With an increase in the pressure of the gas mixture, the current density j increases and the value of h decreases (curve I in Fig. 5, c). At the same time, the depth of the nitride zone hN increases (curve I in Fig. 5, d). Here, too, at a pressure of p = 106.4 Pa, we have a minimum point (point 4*, curve I in Fig. 5, d).

Fig. 6 Dependence of the specific power w on the pressure of the gas mixture p at BATR with autonomous saturation modes (curve I - nitriding at U = 515B = const and curve II - nitriding at j = 7.2A / m² = const)

With a change in the shape of the suspension, j increases with increasing pressure, and also increases, according to the dependences close to a straight line, h and hN (straight lines II in Fig. 5, c and d), which once again indicates the particular importance of taking into account the influence of additional factors on BATR results when designing a suspension, taking into account its shape and surface area, placing parts on the suspension, the presence of grooves, sharp edges on parts, etc.

In autonomous modes of BATR with increasing pressure at U = 515 V = const (points 3, 5 and 8 in Fig. 6), the specific discharge power increases, and at j = 7.2A / m2 = const (points 2, 5 and 9 in Fig. 6) decreases.

The results of X-ray structural analysis also indicate that the structure and phase composition of steel 40Kh depend on the energy characteristics of the discharge. The energy conditions for the main subprocesses (formation of nitrides, surface sputtering, and nitrogen diffusion), as mentioned above, differ significantly.

Consideration of the current-voltage characteristics shows (Fig. 7) that with increasing pressure р1, р2, р3, the values of U and j increase. The indicated dependencies are straightforward. However, in all cases, the values of U and j for modes with interdependent parameters are higher than for stand-alone modes. In this case, with an increase in pressure, the voltage decreases, however, to ensure a glow discharge in the chamber, the value of the specific current density j rises automatically (points 1*, 4* and 7* in Fig. 7).

Fig. 7 Dependences of current-voltage characteristics of BATR on the pressure of the gas mixture

In the autonomous mode of the BATR, with decreasing pressure p, the values of U and j decrease, and at p = 159.6 Pa (point 9 in Fig. 8, a and b) h = hN = 0. At a pressure p = 106.4 Pa U = 515 V, and j = 7.2 A/m² and, accordingly, we obtain the maximum value of hN (Fig. 8, b; point 5).

Fig. 8 Dependences of the depth of the diffusion layer h (a) and the nitride layer hN (b) on the voltage at j = 7.2 A / m² = const; also c and d on the current density j at U = 515B = const

In the case of a fixed value U = 515 V, with an increase in pressure and current density j, the values of h and hN increase, practically along a straight-line relationship (Fig. 8, c and d). In this case, at p = 53.2 Pa and j = 3.2 A/m², there is no nitride layer at all, hN = 0 (point 3 in Fig. 8, d). The latter is explained by the low value of w = 1.65 kW/m² and, as a consequence, the absence of a glow discharge.

The ratio of the intensity of the main subprocesses determines the structure and phase composition of the nitrided layers. Depending on the flow combination of energy parameters, the formation of the nitrided layer can occur in different directions. The intensity of the formation of one or another phase can be different not only in magnitude, but also behind the sign, since the previously formed phase can disappear. Thus, the nitride phase hN, due to further diffusion of nitrogen into the depth of the metal, disappears and a zone of internal nitriding is formed - a nitrogenous solid solution Me [N] (mode 9, a and b), or the nitride layer consists of a small amount of the (Fe4N) phase (mode 3 on Fig. 2, c and d).

According to the results of X-ray structural analysis, at the maximum values of the energy parameters (all modes with interdependent parameters 1*/1**, 4*/4**, 7*/7**, mode 8 and partly 5 with autonomous saturation parameters), a nitrided layer is formed, which consists of (Fe2N), (Fe4N) and (Me [N]) - phases (Fig. 2, mode 7). A decrease in voltage and current density leads to an increase in the phase fraction in the nitride zone of the nitrided layer and, accordingly, to a decrease in the phase (Fig. 2, modes 7, 8). At minimum values of the energy characteristics, a nitride layer does not form on the surface and it consists only of a phase (Fig. 2, mode 9).

Thus, it has been established that under conditions of dry friction for the surfaces of 40Kh steel nitrided at high energy indicators, the wear rate and the running-in period decrease (Fig. 1, b), the latter refutes the statement of K. Keller [13] that the energy characteristics of BATR do not have significant influence on the results of nitriding. On the contrary, the above BATR results allow one to draw completely obvious conclusions about the significant effect of voltage and current density on the physicochemical and tribological properties of nitrided layers. In addition, there is a certain limit of energy parameters below which (modes 9, 6, 3) carrying out BATR processes does not make sense at all, since it leads to negative results, and this despite the fact that the values of operating characteristics (temperature, composition of the gas mixture, its pressure, etc.) nitriding time) remain unchanged. Thus, the set of traditionally fixed operating parameters of the BATR cannot unambiguously characterize the conditions of the nitriding process and be the main one for predicting its results. This fact is also confirmed by the fact that at similar values of the operating parameters, the change of the suspension led to completely different results of nitriding, which is explained by the change in the energy characteristics of the BATR process (Fig. 3... 8).

Conclusion

1. The complex of traditionally fixed values of operating parameters (temperature, composition of the gas mixture, pressure and saturation time) without taking into account energy characteristics (voltage, current density and specific discharge power) significantly reduces the technological capabilities of BATR to achieve the necessary physicochemical properties of metal surfaces specified by conditions exploitation. Taking into account the energy characteristics of BATR, a significant reduction in the energy consumption of the nitriding process is achieved.