离子渗氮化合物层物相调控对耐磨性的影响

目的探索化合物层物相与耐磨性的关系,并实现其有效调控,从而满足不同零部件的服役性能要求。方法选用常用渗氮钢38CrMoAl进行不同氮气比(15%、20%、25%)离子渗氮研究,渗氮温度为510℃,保温4 h。采用光学显微镜、X射线衍射仪、显微硬度计和摩擦磨损试验机对渗氮后的显微组织、物相组成、截面硬度、耐磨性进行了测试和分析。结果在相同的渗氮温度下,调节氮气比可获得不同物相组成的化合物层。在渗氮温度510℃下,氮气比为20%时满足形成γ′相的临界氮势,从而得到γ′单相化合物层。氮气比达到25%时,满足形成ε相的临界氮势,渗氮层中γ′相形成,并动态转变成ε相,使ε相逐渐增多,形成ε+γ′双相化合物层。结论38CrMoAl经不同氮气比离子渗氮后形成了ε+γ′双相化合物层,在较小磨损载荷(200 g)下,具有更优的耐磨性。但在较大磨损载荷(400 g)下,氮气比20%获得的γ′单相化合物层试样磨痕较窄,摩擦系数较小,即在较大磨损载荷下,γ′单相化合物层比ε+γ′双相化合物层表现出更加优异的耐磨性能。该研究可为不同磨损服役条件的零部件离子渗氮工艺设计提供参考。

Effect of Phase Regulation of Plasma Nitriding Compound Layer on Wear Resistance

The work aims to explore the relationship between the phases of compound layer and wear resistance,and realize its effective regulation,so as to meet the service performance requirements of different parts.The common nitriding steel 38CrMoAl was selected for plasma nitriding with different nitrogen ratios(15%,20%,and 25%)at the nitriding temperature of 510℃for 4 hours.The microstructure,phase constituents,cross-sectional microhardness and wear resistance of the nitriding layer were tested and analyzed by optical microscopy(OM),X-ray diffraction(XRD),microhardness tester and friction and wear tester.At the same nitriding temperature,the compound layers with different phase composition could be obtained by adjusting nitrogen ratios.When the nitriding temperature was 510℃and the nitrogen ratio was 20%,the critical nitrogen potential for the formation of theγ′phase was satisfied,thus theγ′single phase compound layer was obtained.When the nitrogen ratio reached 25%,the critical nitrogen potential for the formation of theεphase was satisfied.The dynamic formation and transformation of theγ′phase in the nitriding layer into theεphase increased theεphase gradually andε+γ′biphasic compound layer was obtained.Theε+γ′biphasic compound layer formed by 38CrMoAl after plasma nitriding with different nitrogen ratios has better wear resistance at a small wear load of 200 g.However,when the wear load is 400 g,the wear scar and the friction coefficient ofγ′single phase compound layer are narrower and smaller at 20%nitrogen ratio.That is to say,under the heavier wear load,the wear resistance of theγ′single-phase compound layer is better than that of theε+γ′biphasic compound layer.This study can provide reference for the design of ion nitriding process for parts with different wear and service conditions.