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Compared to conventional plasma nitrocarburizing the active screen plasma nitrocarburizing technology reduces significantly the risk of soot production and cementite precipitation in the compound layer of nitrocarburized materials. However, in long-time treatments, the uncontrollable contamination even up to full saturation of the metallic active screen and of the walls of the used plasma reactor with carbon compounds is still a remaining factor of uncertainty. It may result in an increased carbon concentration or even in an appearance of the cementite phase in the compound layer of the treated steel surface, as in the case of 42CrMo4 (AISI 4140). The absolute concentration of hydrogen cyanide (HCN), in situ monitored by tunable diode laser absorption spectroscopy, and the emission intensity of the CN (0–0) band of the violet system at a wavelength of λ = 388 nm, recorded by optical emission spectroscopy, were found to be reliable parameters to control the carburizing potential of the nitrocarburizing plasma. A close relationship was found between (i) the concentration of HCN and the CN band emission intensity with (ii) the level of the methane admixture in the feed gas and the time-dependent contamination effects of the active screen and other inner reactor surfaces with carbon compounds. Therefore, this relation could serve as a basis for an in-line control of the carburizing activity in plasma nitrocarburizing processes with methane admixture using an active screen. [ABSTRACT FROM AUTHOR]

The combined treatment of electron beam (EB) cladding and subsequent nitrocarburizing of duplex stainless steels aims at enhancing the wear behavior and simultaneously maintaining their outstanding corrosion resistance. By means of electron beam cladding using a Co-based wire surface coatings are generated that exhibit enhanced surface hardnesses up to 500 HK0.01 as well as improved corrosion properties. The nitrocarburizing of these coatings results in surface layers with hardness values above 1100 HK0.01 and a thickness of about 10 μm. For treatment temperatures of up to 420 °C these layers consist of, among other phases, expanded austenite and are free of chromium precipitations. The wear coefficient is significantly reduced and the corrosion resistance is maintained. The functional effectiveness of such surface matrix compounds is based on the combination of high surface hardness and good corrosion resistance, which are maintained, even if layer defects occur within the nitrocarburized layer, due to the improved corrosion behavior of the EB coating underneath. [ABSTRACT FROM AUTHOR]

These multi-combined surface treatments lead to a significant improvement in load-supporting capacity. Critical load values of cohesive failure measured by scratch tests are tripled when compared to the individual treatment of PVD, and increased by at least 20% in comparison to the duplex treatments of EBH+PVD or PN+PVD. The metallurgical compatibility of the single treatments is essential for the success of combined treatments. Material-specific limitations are defined, which exclude failure due to crack initiation, the occurrence of retained austenite, and tempering effects. Based on the model wear-test assembly block-on-cylinder, it was proved, that the specific wear rate of multi-combined treated specimens is reduced about 20-50% while wear of counterpart components is decreased as well. The triplex surface heat treatment introduced opens up new prospects for highly-loaded components and tools. [ABSTRACT FROM AUTHOR]

Dry sliding friction and wear behavior of nitrided and non-nitrided spray-formed Al alloys against AISI52100 steel were investigated using a linear-reciprocating ball on flat configuration under different normal loads. In case of nitrided spray-formed Al alloys, an increase in the applied normal load leads to a steady reduction of the stationary stage of the coefficient of friction depending on the sustainability of the AlN/Al compound. With regard to the nitride layer, thickness-specific wear regimes are distinguished for both spray-formed Al alloys. Nitrided spray-formed AlSi alloys show mild abrasive wear independent of normal load in case of AlN layers with up to 3 µm thickness. The layers exhibit an increased wear resistance compared to the non-nitrided condition for all applied test loads. Thick AlN layers > 4 µm show a steep increase in wear rate at loads exceeding 10 N, indicating a severe adhesive wear. These layers fail due to nitride layer delamination. Nitrided spray-formed AlMg alloys show mild abrasive wear for thin AlN layers < 4 µm up to normal loads of 12 N. Thick AlN layers almost immediately fail upon the initiation of the sliding contact due to crack formation within the nitride layer. [ABSTRACT FROM AUTHOR]