Dry wear and friction behaviour of plasma nitrided Ti–6AL–4 V alloy after explosive shock treatment

The unlubricated wear behaviour of explosive shock treated and, subsequently plasma nitrided Ti–6Al–4 V alloy was studied using a ball-on-disc wear tester. Plasma nitriding was carried out at three different temperatures (700, 800 and 900 °C) for 3, 6, 9 and 12 h. Plasma nitriding after explosive shock treatment enabled a reduction in the wear rate of two orders of magnitude. Detailed investigations of this improved wear performance dependent on the nitriding temperature and time were carried out. The friction and wear data showed a clear breakthrough transition from the nitrided layer to the core of the Ti–6Al–4 V alloy matrix. The lowest wear volume was obtained for the sample, nitrided at 900 °C for 12 h, especially at loads of 2.5, 5 and 7.5 N. Obviously, the hard nitride layers were intimately associated with low wear rate, providing a smooth low friction surface. The coefficient of friction reduced from 0.46 to 0.2 due to a thick and hard compound layer resulting from a high nitrogen diffusion rate caused by explosive shock treatment that expected to increase point defects in the alloy. Detailed examination of the wear tracks showed that plasma nitriding changes the mechanism of wear from one of adhesion for untreated Ti–6Al–4 V to both delamination and mild abrasive.     

Several plasma diffusion processes for improving wear properties of Ti6Al4V alloy

Different kinds of diffusion processes, plasma nitriding, oxidizing and oxynitriding as of a combination of other two, have been applied to Ti6Al4V alloy to evaluate the effect of treatment times (1 and 4 h) and temperatures (650 and 750 °C) on wear properties of the alloy. It was observed that a hard modified layer was produced on the surface of the alloy after each diffusion process. While TiN and Ti₂N phases form in the modified layer with plasma nitriding, mainly TiO₂ phase forms after plasma oxidizing treatment. The wear tests performed at different normal loads showed that all treated samples, except for nitrided and oxidized at 650 °C for 1 h, exhibited higher wear resistance than untreated Ti6Al4V alloy. The plasma nitrided samples showed adhesive wear. On the other hand, while the plasma oxidizing samples displayed adhesive wear at lower loads, wear mechanism changed to abrasive wear as the load increased because the oxide film which covers the surface was broken during the sliding at higher loads.     

Multi-pass scratch test behavior of modified layer formed during plasma nitriding

316L stainless steel and Ti6Al4V alloy were plasma nitrided at different treatment parameters, and the wear behaviors of the modified layers formed on the surface during nitriding were investigated by multi-pass scratch test. Phase structure and cross-sections of modified layers were also examined with XRD and SEM. While a single modified layer formed on surface of the 316L stainless steel, both modified and diffusion layers were observed on the surface of the Ti6Al4V alloy after nitriding. As a result, it was observed that phase structure and thickness for modified layers of 316L stainless steel and Ti6Al4V alloy, respectively, were the significant parameters for friction coefficient and wear rate. In addition, diffusion layer formed during the nitriding process caused on increase of wear resistance of Ti6Al4V alloy by supporting the modified layer on the surface.     

渗氮GCr15钢在含氮硼酸酯添加剂润滑油作用下的摩擦学性能

针对提高滚动轴承使用寿命的问题,提出离子渗氮处理与添加剂结合的解决办法。用等离子渗氮炉在GCr15轴承钢表面制备了渗氮层,并用扫描电子显微镜(Scanning electron microscope, SEM )、X射线衍射仪(X-ray diffractometer, XRD)和显微硬度计观测了渗层的形貌、相结构和硬度变化。利用四球摩擦磨损试验机对比考察渗氮钢和未渗氮钢在含氮硼酸酯润滑条件下的摩擦学性能,并用X射线光电子能谱仪(X-ray photoelectron spectroscope, XPS)分析摩擦反应膜的成分与化学结合态。结果表明,渗氮层与润滑油添加剂之间发生了意想不到的良好交互作用,渗氮钢在质量分数为1.25%氮硼酸酯的润滑条件下表现出最低的摩擦因数和磨斑直径,比未渗氮钢分别降低了34%和45%;分析证明,渗氮层的摩擦表面生成了高BN质量分数的摩擦反应膜是获得优异摩擦学性能的主要原因,而在未渗氮钢摩擦表面未检测到BN。     

Influence of plasma nitriding on fretting wear behaviour of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V samples at 520 °C in two environments (pure nitrogen and a mixture of nitrogen and hydrogen in the ratio of 3:1) for two different time periods (4 and 18 h). Fretting wear tests were conducted on unnitrided and nitrided samples for 50,000 cycles using alumina ball counterbody. Plasma nitriding reduced the tangential force coefficient of Ti–6Al–4V. The samples nitrided for 4 h exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided for 18 h. The samples nitrided in nitrogen–hydrogen mixture environment exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided in pure nitrogen. The samples plasma nitrided in nitrogen–hydrogen mixture for 4 h exhibited the highest hardness and the lowest tangential force coefficient. The wear volume and specific wear rate of the plasma nitrided samples were lower than those of the unnitrided samples. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume and specific wear rate at different loads.     

38CrMoAl液压柱塞无白亮层低温离子渗氮工艺研究

对38CrMoAl液压柱塞进行低温离子渗氮,研究不形成白亮层的工艺条件。采用金相显微镜、X射线衍射仪、显微硬度计、摩擦磨损试验机对处理后的38CrMoAl钢显微组织、截面硬度、渗层脆性、耐磨性进行了分析。研究结果表明,相比于510℃常规离子渗氮工艺,38CrMoAl钢经450℃低温离子渗氮工艺处理后无白亮层产生,X射线衍射分析表明表层无γ'-Fe₄N相生成。同时,38CrMoAl钢经450℃低温离子渗氮工艺处理后,不仅截面硬度满足使用要求,而且渗层脆性显著降低,压痕周围均无裂纹产生。耐磨性研究表明,在较大载荷下,450℃低温离子渗氮后耐磨性比510℃常规离子渗氮好。     

离子硫氮复合渗42CrMo钢的耐磨性和抗咬合性研究

研究了离子硫氮复合渗对42CrMo钢的耐磨性和抗咬合性的影响。数据表明，与42CrMo钢调质态和单一离子渗氮工艺状态相比，该钢经离子硫氮复合渗处理后可明显提高钢的耐磨性和抗咬合性。通过对渗层的组织结构分析，探讨了硫氮复合渗层对提高42CrMo钢的耐磨性和抗咬合性的作用机理。     

Friction and rolling–sliding wear of DC-pulsed plasma nitrided AISI 410 martensitic stainless steel

In the present work, industrial-scale DC-pulsed plasma nitriding for 20 h at 673 K was used to improve the wear resistance of an AISI 410 martensitic stainless steel. The tribological behaviour was studied and compared to the behaviour of the same steel in as-received condition.Pin-on-disc dry tests, using an alumina ball as counter-body, were carried out to determine the evolution of the friction coefficient. The wear resistance was investigated using an Amsler-disc-machine, employing a dry combined contact of rolling–sliding with three different applied loads. The wear mechanisms involved during rolling–sliding of unnitrided and plasma nitrided steels were investigated by microscopic observation of the surfaces, the corresponding cross-sections and the produced wear debris.The combination of different wear mechanisms taking place in the wear process of unnitrided and nitrided materials were discussed and analyzed. In contrast to the unnitrided steel, DC-pulsed plasma nitrided samples presented an improvement in the friction coefficient and the wear rate.     

The Effect of Plasma Nitriding on the Tribology of Perfluoropolyether Grease-Lubricated 2Cr13 Steel Couples in Vacuum

A 2Cr13 steel was modified by plasma nitriding. The microstructure, phase composition and microhardness of the nitrided samples were examined. The friction and wear behaviour of the nitrided and unnitrided samples sliding against self-mating under PFPE grease-lubricated conditions in vacuum was investigated on a pin-on-disk type tribometer, with the interactions among the nitrided layer and grease to be focused on. The morphologies of the worn surfaces were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy. The chemical compositions of grease samples taken from the worn surfaces were analyzed by Fourier transform infrared spectroscopy (FTIR). Results show that the nitrided steel has better friction-reducing and anti-wear abilities than the unnitrided one under PFPE grease-lubricated conditions. In the former case, the wear of nitrided steel shows a transition from mild abrasive wear to fatigue one with increasing normal load. In the latter case, wear mechanism of unnitrided steel under all load applied is a combination of the severe abrasion and fatigue.     

Tribological properties of plasma nitrided stainless steel against SAE52100 steel under ionic liquid lubrication condition

1Cr18Ni9Ti stainless steel was modified by plasma nitriding. The phase composition of the plasma nitrided layer was examined by means of X-ray diffraction. The friction and wear properties of the modified and unmodified 1Cr18Ni9Ti stainless steel specimens sliding against SAE52100 steel under the lubrication of ionic liquid of 1-ethyl-3-hexylimidazolium hexafluorophosphate (L-P308) and poly α-olefin (PAO) were investigated on an Optimol SRV oscillating friction and wear tester, with the interactions among the modified surface layer and the ionic liquids and PAO to be focused on. The morphologies of the worn surfaces were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces of the modified steel surfaces were examined by means of X-ray photoelectron spectroscopy. Results showed that the modified sample had better anti-wear abilities than the unmodified one, but the modified sample had a slightly higher friction coefficient than the untreated one. This was partly attributed to the change in the hardness and phase composition of the stainless steel surfaces after plasma nitriding and tribochemical reactions between the steel and the lubricant. The resultant surface protective films composed of various tribochemical products together with the adsorbed boundary lubricating film contributed to reduce the friction and wear.     

离子渗氮气氛对TC4钛合金组织与性能的影响

研究了在不同气氛下进行离子渗氮对TC4钛合金渗氮层的组织与性能的影响。进行了金相组织检查,显微硬度测定,X射线结构分析,磨损试验与渗氮层氧含量测定。试验结果表明,保温时的气氛对控制渗氮层质量有较大的影响     

Wear resistance and anti-sticking properties of duplex treated forming tool steel

The aim of this work was to investigate the potential of using hard physical vapour deposition (PVD) coatings on forming tools, as well as to determine the influence of plasma nitriding on the load-carrying capacity and wear resistance of coated tool surfaces. A load-scanning test rig was used for evaluation, where duplex treated cold work tool steel samples were loaded against soft austenitic stainless steel and hardened ball bearing steel, respectively. Four different coatings (TiN, TiB₂, TaC and DLC) and two substrate treatments (hardening and plasma nitriding in two different gas mixtures) were included.Plasma nitriding alone significantly improved the friction, wear, and anti-sticking properties of the tool steel. PVD coating, and especially PVD coating of nitrided tool steel further improved the performance. Therefore, from the point of view of tool life as well as work peace surface quality, the DLC coating with its excellent anti-sticking properties and sufficiently good wear resistance represent the best solution for forming tool applications of austenitic stainless steel.     

Structure and tribological behavior of submicrocrystalline titanium modified with nitrogen ions

The influence of combined treatment including intensive plastic deformation and ion-beam nitriding on the structure and tribological behavior of VT1–00 titanium alloy is studied. Intensive plastic deformation of titanium is shown to result in the formation of submicrocrystalline structure and 50–60% greater hardness of the alloy with tribological properties remaining unchanged. Implantation of nitrogen ions into titanium at 620–820 K results in the formation of a hard solution in the matrix α phase, which provides an increase in the microhardness of the modified layer up to 3500–3700 MPa and an increase in the alloy wear resistance by about 30 times, as well as a decrease in the coefficient of friction by 40%.     

Laboratory assessment of wear on nitrided surfaces of dies for hot extrusion of aluminium

A newly designed “block-on-cylinder” wear resistance testing rig, which allows testing at higher contact pressures than conventional testing methods, was used to elucidate the effect of an iron nitride compound layer (white layer) on the wear resistance of nitrided dies used for hot extrusion of aluminium (Al). The tested dies (AISI H13) with various nitrided microstructures were provided by different manufacturers of equipment for plasma and gas nitriding. The wear surfaces were analysed by SEM, BEC, micrography and roughness measurements. It was found that the iron nitride compound layer is chemically more stable against hot Al in comparison to die material. Deterioration of the compound layer begins with cracking, and as a consequence, its spalling from the nitrided surface. A high thickness of the compound layer combined with a low nitriding depth leads to its earlier spalling and vice versa. Due to the increased roughness at the removal sites, accelerated chemical attack by hot Al takes place. Comparative and simultaneous testing of two nitrided samples was carried out.     

Effect of nitriding on wear resistance of iron alloys with various lattice types

The paper considers the characteristics of the formation of the wear-resistant structure of nitrided model alloys with bcc and fcc lattices: Fe-Mo, Fe-Cr, Fe-Al, Fe-Ni-Cr, Fe-Ni-Al, Fe-Ni-Ti, and Fe-Ni-Cr-Al-Ti. The relationships between the structure characteristics of the nitrided layer and the wear resistance of the alloys are found. The maximal wear resistance of the alloys with the bcc lattice of the matrix is shown to be attained when incoherent particles of nitrides of the alloying elements appear; the maximal hardness corresponds to the alloy that contains coherent nitrides. In the alloys with the fcc lattice, the maximal hardening under nitriding and the maximal wear resistance are achieved at the stage that precedes the rupture of the coherent bond between the nitride and the matrix. The relationships between the structure characteristics of the nitrided layer and the wear resistance are discussed from the viewpoint of the formation of a wear-resistant structure state of the alloys.     

Tribological properties of plasma nitrided AISI 4140 steel under dry and lubricated sliding conditions

In this investigation, the microstructural, mechanical and tribological properties of plasma and pulse plasma nitrided AISI 4140 steel have been investigated in comparison to hardened steel. The influence of nitriding case depth, as well as the presence of a compound layer, have been tribologically examined for both dry and lubricated sliding. Testing was carried out on a pin‐on‐disc machine in which surface‐treated pins were mated to hardened ball bearing steel discs. The surface treated samples were characterised using metallographic, SEM, microhardness and profilometric techniques, before and after wear testing. The resulting wear loss and coefficient of friction were monitored as a function of load and of test time. The results showed improved tribological properties of the AISI 4140 steel after plasma and pulse plasma nitriding as compared to the hardened steel, in both dry and lubricated sliding. However, the compound layer should be removed from the surface, either by mechanical means or by decreasing the amount of nitrogen in the nitriding atmosphere, in order to avoid impairment of the tribological properties by fracture of the hard and brittle compound layer, followed by formation of hard abrasive particles.     

Tribological behavior of intermetallic Fe<Subscript>3</Subscript>Al alloy treated by intensive beams of nitrogen ions

The structure, phase composition, and tribological behavior of intermetallic Fe₃Al alloy subjected to ion-beam nitriding at 670–870 have been studied. The ion-beam treatment of the alloy proved to result in nitrogen-modified layers of up to 15–18 nm thick and microhardness up to 13200 MPa. The formation of nitride AlN phases with cubic and hexagonal lattices was registered in the nitrided layers. The formation of aluminum nitrides with the cubic lattice of NaCl structural type is shown to increase the wear resistance of Fe₃Al alloy 25–28 times, and with the hexagonal one it increases 5–8 times.     

NH4Cl对TiAl基合金渗氮的影响

介绍了NH4Cl对TiAl基合金渗氮的影响以及渗氮后其渗层的组织特点。结果表明，在一定的温度和时间范围内，NH4Cl对TiAl基合金渗氮有显著的催化作用，主要表现在渗层厚度的增加、渗氮速率的提升和合金表面显微硬度值的增大。     

Effect of composition and structure of nitrided iron alloys on wear resistance under friction and sliding

Characteristic features of the formation of the wear-resistant structure of the nitrided model alloys with body-centered cubic (bcc) and face-centered cubic (fcc) lattices are studied, including Fe-Mo, Fe-Cr, Fe-Al, Fe-Ni-Cr, Fe-Ni-Al, Fe-Ni-Ti, and Fe-Ni-Cr-Al-Ti. Interrelations are established between the parameters of the structure of the nitrided layer and the wear resistance of alloys. It is shown that, in alloys with the bcc lattice, maximum wear resistance is achieved by the formation of incoherent particles of nitrides of alloying elements, and the maximum hardness can be found in the alloy with coherent nitrides. In alloys with the fcc lattice, maximum hardening during nitriding and wear resistance are achieved at the stage preceding the rupture of coherent communication of the nitride with the lattice. Interconnections of characteristics of the structure of the nitrided layer and the wear resistance are discussed in the context of the formation of the wear-resistant structural state of alloys.     

Tribocorrosion of Pulsed Plasma-Nitrided CoCrMo Implant Alloy

In the present study, a forged CoCrMo (ISO 5832-12) has been subjected to pulsed plasma treatment in a N₂/H₂ atmosphere at low temperatures (below 500 °C). This treatment resulted in the formation of a layer composed by dispersed chromium nitride particles in a N-enriched metal matrix. The materials were tested for corrosion and tribocorrosion performance in 0.9 wt% NaCl at room temperature under controlled electrochemical conditions. After the treatment, the alloy loses its passive nature. The electrode potential was found to critically affect the corrosion and the tribocorrosion rates. In the nitrided alloy, a significant increase of corrosion rate was found at high potentials, while tribocorrosion was determined mainly by mechanical wear and not affected by potential. On the other hand, the untreated CoCrMo alloy exhibited stable corrosion over a wide range of potentials. Its tribocorrosion rate was similar to the nitrided alloy samples at low potentials, but it increased dramatically at high potentials where passivity triggered severe wear-accelerated corrosion and promoted mechanical wear. The present study shows that the electrochemical conditions determine material deterioration and should therefore be considered when selecting materials for tribocorrosion applications such as biomedical implants.