Samples of AISI 409 were thermochemically treated by the Solution Heat Treatment after Plasma Nitriding (SHTPN) process. SHTPN process consisted of a nitriding step followed by solution annealing at 1100 °C and rapid cooling down to room temperature. The second cycle of quenching (950 or 1050 °C), followed by tempering (250, 450, or 650 °C), was performed sequentially to SHTPN. Lubricated reciprocating tests were employed to analyze friction and wear behaviors. A bearing steel ball was used as a counterpart. The analysis of worn surfaces was assessed using optical interferometry and depth-sensing indentation. The last technique allows determining the work hardening caused by the wear process. Friction behavior was related to the deformation component: the higher the hardening, the lower the friction coefficient. Abrasion is the primary mechanism observed in all specimens, but there is a transitional behavior that depends on the original hardness of the surface. Samples with a similar hardness of bearing ball presented delaminated regions caused by highly deformed thin layer fatigue. Amongst SHTPN conditions NS-Q950-T2 and NS-Q1050-T2 presented the best balance of wear and corrosion performances.
Nickel-aluminum bronzes (NABs) comprise a versatile group of copper-based age hardenable quaternary alloys. Their composition usually comprises aluminum, nickel, iron, and manganese, besides copper. These alloys have a large range of applications, from architectural use to naval propellers. In the present work, a case study of a specific NAB alloy of technical importance was performed aiming to investigate the difference in wear resistance between samples that were aged and samples that received a novel hybrid aging + nitriding treatment carried out on a plasma immersion ion implantation (PIII) apparatus. Both regular aging and the hybrid treatment were carried out for solution-treated coin-shaped specimens, with martensitic matrix, in a PIII chamber under a nitrogen-based atmosphere. Three different voltage biases, 8, 10, and 12 kV, resulted in three distinct treatment temperatures, 370, 400 and 470 ºC, for treatment times of 180 and 90 min, being the latter (90 min) used together with the smaller voltage (370 ºC) for comparison purposes. From the coin-shaped sample, it was possible to study the two distinct treatments: i) the flat-surface-side exposed to plasma was subjected to the hybrid treatment; ii) the other flat-side (directly supported on the sample holder) was only aging-treated (hereafter termed ‘aged only’). Such methodology allowed to infer the bulk effects on the surface modification process. The XRD patterns of the hybrid-mode treated (hereafter termed ‘aged + nitrided’) surfaces showed formation of nitrogen-expanded phases, these surfaces showing hardness gains varying on the 11-27% range when compared to the respective surfaces aged only. Scratch tests, in association with hardness and elastic modulus measurements, showed the role of the aging on the elasto-plastic response of both aged only and aged + nitrided surfaces. The nitriding resulted in significant gains of wear resistance for PIII carried out at the lowest temperatures: 43% and 41% less volume loss than the respective aged only surfaces for the treatments at 370 °C for 90 min and 180 min, respectively. Differently, the treatments at the highest temperature (450 °C) resulted in the worst wear performances, since the bulk over-aging surpassed any strength delivered by nitriding.
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