Wear resistant multilayer nanocomposite WC1−x/C coating on Ti–6Al–4V titanium alloy

A significant improvement of tribological properties on Ti–6Al–4V has been achieved by developed in this study multilayer treatment method for the titanium alloys. This treatment consists of an intermediate 2 μm thick TiC_xN_y layer which has been deposited by the reactive arc evaporation onto a diffusion hardened material with interstitial O or N atoms by glow discharge plasma in the atmosphere of Ar+O₂ or Ar+N₂. Subsequently, an external 0.3 μm thin nanocomposite carbon-based WC_1−x/C coating has been deposited by a reactive magnetron sputtering of graphite and tungsten targets. The morphology, microstructure, chemical and phase compositions of the substrate material after treatment and coating deposition have been investigated with use of AFM, SEM, EDX, XRD, 3D profilometry and followed by tribological investigation of wear and friction analysis. An increase of hardness in the diffusion treated near-surface zone of the Ti–6Al–4V substrate has been achieved. In addition, a good adhesion between the intermediate gradient TiC_xN_y coating and the Ti–6Al–4V substrate as well as with the external nanocomposite coating has been obtained. Significant increase in wear resistance of up to 94% when compared to uncoated Ti–6Al–4V was reported. The proposed multilayer system deposited on the Ti–6Al–4V substrate is a promising method to significantly increase wear resistance of titanium alloys.     

Failure mechanisms of a PCD tool in high-speed face milling of Ti–6Al–4V alloy

High-speed milling tests were carried out on Ti–6Al–4V titanium alloy with a polycrystalline diamond (PCD) tool. Tool wear morphologies were observed and examined with a digital microscope. The main tool failure mechanisms were discussed and analyzed utilizing scanning electron microscope, and the element distribution of the failed tool surface was detected using energy dispersive spectroscopy. Results showed that tool flank wear rate increased with the increase in cutting speed. The PCD tool is suitable for machining of Ti–6Al–4V titanium alloy with a cutting speed around 250 m/min. The PCD tool exhibited relatively serious chipping and spalling at cutting speed higher than 375 m/min, within further increasing of the cutting speed the flank wear and breakage increased greatly as a result of the enhanced thermal–mechanical impacts. In addition, the PCD tool could hardly work at cutting speed of 1,000 m/min due to the catastrophic fracture of the cutting edge and intense flank wear. There was evidence of workpiece material adhesion on the tool rake face and flank face in very close proximity to the cutting edge rather than on the chipped or flaked surface, which thereby leads to the accelerating flank wear. The failure mechanisms of PCD tool in high-speed wet milling of Ti–6Al–4V titanium alloy were mainly premature breakage and synergistic interaction among adhesive wear and abrasive wear.     

激光熔覆原位自生Ti-Al-Si复合涂层的微观组织和高温抗氧化性能

为提高钛合金的高温抗氧化性能,采用激光熔覆原位自生技术,在TC4钛合金表面自行设计并制备了原子百分比为Ti∶Al∶Si=41∶41∶18和Ti∶Al∶Si=35∶35∶30的两种涂层。通过XRD、OM、SEM表征了涂层的微观组织和物相组成;借助管式电阻炉测试了涂层和基体试样在800℃×24h×5次循环氧化条件下的高温抗氧化性能;结合氧化增重和氧化动力学曲线分析了涂层的高温抗氧化机理。结果表明,涂层主要由Ti5Si3、Ti7Al5Si12、Ti3Al、TiAl和TiAl3等物相组成。涂层中没有出现一般激光熔覆所产生的外延生长柱状晶组织,全部为细小等轴晶。在800℃×24h×5次循环氧化条件下,TC4基材单位面积的氧化增重约为35.1mg·cm-2,涂层的约为2.8mg·cm-2和3.3mg·cm-2。两种涂层的高温抗氧化性能较钛合金基材分别提高了12.5倍和10.6倍。激光熔覆原位自生Ti-Al-Si复合涂层能明显改善TC4钛合金的高温抗氧化性能。涂层抗氧化性改善的机理,一方面是表面生成了连续致密的TiO2、Al2O3、SiO2氧化层,阻碍了氧扩散;另一方面是提高了氧化层的黏附性,使氧化层不易从涂层表面剥落,对涂层未氧化部分起到了很好的保护作用。     

Influence of Calf Serum on Fretting Behaviors of Ti–6Al–4V and Diamond-Like Carbon Coating for Neck Adapter–Femoral Stem Contact

Influences of newborn calf serum on the fretting behaviors of Ti–6Al–4V and diamond-like carbon coating were investigated using a fretting-wear test rig with a cylinder-on-flat contact. The results indicated that, for the Ti–6Al–4V/Ti–6Al–4V contact, the friction coefficients were high (0.8–1.2) and the wear volumes presented an increase with the increase in the displacement amplitude under dry laboratory air conditions. Under serum-liquid conditions, the Ti–6Al–4V/Ti–6Al–4V contact presented significantly larger wear volumes under the displacement of ±?40 µm; however, it presented significantly lower friction coefficients (0.25–0.35) and significantly smaller wear volumes under the displacement of ±?70 µm. For the DLC coating/Ti–6Al–4V contact, the coating response wear maps could be divided into two areas: the coating working area (low normal force conditions) and the coating failure area (high normal force conditions). In the coating working area, the DLC coating could protect the substrate with low friction, low wear volume, and mild damage in the coating. The presence of serum had a positive influence on the tribological performance of the DLC coating. Furthermore, the positive influence was more significant under larger displacement amplitudes condition.     

A study on laser assisted machining of Ti10V2Fe3Al alloy with varying laser power

Laser-assisted machining (LAM) is a promising technique to improve the machinability of various difficult-to-machine materials such as steels, nickel and titanium alloys and metal-matrix composites. Most of the research studies are focused on analyzing the effect of various cutting parameters such as cutting speeds, feed rates and depth of cut at a constant laser power despite being reported that the maximum benefit of the LAM technique can be realised when all parameters including laser power are optimised. Therefore, the primary objective of this paper is to assess the effect of laser power on the cutting temperature and cutting forces including force fluctuations during the machining of Ti10V2Fe3Al alloy. A cutting force reduction of at least 10 % was found using the assistance of a 1,600 W laser beam between cutting speeds of 55–140 m/min. Nevertheless, it was concluded that a power of 800–1200 W for the laser beam is best suited during LAM of Ti10V2Fe3Al alloy within a cutting speed range of 55–100 m/min. Further, higher cutting speeds were recommended when employing a higher power laser beam to avoid problems such as chatter and chip pile-up.     

Mechanical and tribological properties of Cr–Nb double-glow plasma coatings deposited on Ti–Al alloy

Double-glow plasma (DGP) coatings are recommended for metallic components to mitigate the damage induced by complex working conditions in previous studies. In this paper, Nb-rich (Cr–Nb₄) and Cr-rich (Cr₄–Nb) -alloyed layers were formed onto the Ti–Al substrate via a DGP process to enhance its wear resistance. Scratch and Nano-indentation tests were used to evaluate the mechanical properties of the coatings. The tribological behaviour of the coatings were investigated using a pin-on-disc tribometer by rubbing against the GCr15 ball. Results from surface analysis techniques showed that the coatings mainly comprised Cr, Nb and Cr₂–Nb phases, and were well bonded to the substrate. The hardness of the Cr–Nb₄ coating was 11.61GPa and the Cr₄–Nb coating was 9.66 GPa which all higher than that of the uncoated Ti–Al which was 5.65 GPa. However, the critical load of the Cr₄–Nb coating ~21.64 was higher than that of the Cr–Nb₄ coating ~17.6. And the specific wear rate of Cr–Nb₄ coating, Cr₄–Nb coating and uncoated Ti–Al were 3.54 × 10^?4, 0.01 × 10^?4 and 1.53 × 10^?4mm³ N^?1 m^?1_, respectively. The low-wear mechanism of the coatings is discussed in detail in this paper.     

Corrosion and erosion performance of HVOF/TiAlN PVD coatings and candidate materials for high pressure gate valve application

The main objective of this paper is to study the slurry erosion and corrosion behavior of WC10Co4Cr, Armcore ‘M’ Stellite 6 and 12 HVOF coatings, TiAlN PVD coating, selected steels, such as X20Cr13, 17Cr–4Ni pH steel and Ti6Al4V titanium alloy alongwith conventional hard weld deposits of Stellite 6 and 21. The slurry erosion studies were carried out at 60° angle of impingement for the velocities in the range of 15–20 m/s using mineral sand of −40 to +80 mesh. The corrosion studies were carried out as per ASTM B 117-73 for 100 h. During slurry erosion testing, WC10Co4Cr HVOF along with TiAlN PVD coating are found out, to be the best coating materials followed by HVOF coating of Armcore ‘M’ material. However, for corrosion, Ti6Al4V, Stellite 6 and 21 hard weld deposits and 17Cr–4Ni pH steel turned out to be the best materials followed by HVOF coating of Stellite 6 and 12. HVOF coatings of WC10Co4Cr and Armcore ‘M’ materials corroded significantly, however, TiAlN PVD coating corroded very badly even after 24 h of testing.     

Increasing the tribological performances of Ti–6Al–4V alloy by forming a thin nanoporous TiO2 layer and hydroxyapatite electrodeposition under lubricated conditions

In this study, comparative investigation of (i) untreated Ti–6Al–4V alloy, (ii) nanoporous thin TiO₂ layer formed by controlled anodic oxidation and (iii) electrodeposited hydroxyapatite coatings into porous oxide layer was carried out for evaluation of sliding-wear performances in a bio-simulated environment. Wear mechanisms, wear volumes and friction coefficients of the three types of surfaces under lubricated conditions in a bio-simulated solution were recorded and analyzed. The results presented herein show that, under the investigated tribocorrosion conditions (under reciprocating sliding), both surface treatments applied have improved the wear resistance and friction coefficients as compared to the untreated Ti–6Al–4V alloy surface.     

选区激光熔化工艺参数对Ti6Al4V粉末成型性的影响

以Ti6Al4V钛合金粉末为研究对象,在单层扫描和单道扫描实验的基础上,研究SLM工艺参数对Ti6Al4V合金材料成型性的影响,并进行了块体成型实验,通过设计正交试验及观察试样的形貌和致密度分析,最终得到Ti6Al4V合金粉末SLM块体成型的最佳工艺参数为:激光功率400W、搭接率1、扫描速度750mm/min,其致密度可以达到96.17％.     

Backscattered electron imaging and electron backscattered diffraction in the study of bacterial attachment to titanium alloy structure

The application of secondary electron (SE) imaging, backscattered electron imaging (BSE) and electron backscattered diffraction (EBSD) was investigated in this work to study the bacterial adhesion and proliferation on a commercially pure titanium (cp Ti) and a Ti6Al4V alloy (Ti 64) with respect to substrate microstructure and chemical composition. Adherence of Gram‐positive Staphylococcus epidermidis 11047 and Streptococcus sanguinis GW2, and Gram‐negative Serratia sp. NCIMB 40259 and Escherichia coli 10418 was compared on cp Ti, Ti 64, pure aluminium (Al) and vanadium (V). The substrate microstructure and the bacterial distribution on these metals were characterised using SE, BSE and EBSD imaging. It was observed that titanium alloy‐phase structure, grain boundaries and grain orientation did not influence bacterial adherence or proliferation at microscale. Adherence of all four strains was similar on cp Ti and Ti 64 surfaces whilst inhibited on pure Al. This work establishes a nondestructive and straight‐forward statistical method to analyse the relationship between microbial distribution and metal alloy structure.     

Severe-to-Mild Wear Transition of Titanium Alloys as a Function of Temperature

Dry sliding wear behaviors of Ti–6Al–4V and Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloys (code-named TC4 and TC11, respectively) against AISI 52100 steel under a load of 50–250 N at 25–600 °C were systematically investigated. For two titanium alloys, a severe-to-mild wear transition occurred with an increase in temperature. The critical transition temperatures of TC4 and TC11 alloys were 400 and 300 °C, respectively. Below the critical temperature, titanium alloys showed poor wear performance. As the temperature surpassed the critical temperature, the extremely low wear rates demonstrated excellent elevated-temperature wear performance of titanium alloys in the titanium alloy/steel tribo-system. The wear transition was characterized with the appearance of continuous, hard tribo-layer containing more oxides, especially Fe₂O₃, which showed a pronounced wear-reduced role. Adhesive and abrasive wear predominated in the severe wear regime; oxidative mild wear prevailed in the mild wear regime. Adhesive wear, abrasive wear and oxidative mild wear cooperated at the critical transition temperatures.     

热处理条件下激光原位合成高铌Ti-Al金属间化合物复合涂层的微结构特征

为了提高钛合金的高温抗氧化性能,推动钛合金在高温和复杂工况环境下的进一步工程应用,利用高能激光束作用下Ti、Al、Nb三种元素混合粉末之间的原位反应在BT3-1钛合金表面制备了高温抗氧化的高铌Ti-Al金属间化合物复合涂层。针对原位反应所制备涂层存在的缺陷,通过自行设计的热处理工艺优化了涂层和界面微观组织。借助光学显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)分析了热处理前后复合涂层的物相结构及显微形貌。结果表明:热处理前的涂层主要由单质Nb、金属间化合物γ-TiAl、α_2-Ti_3Al、Ti_3Al_2等物相组成;热处理后的复合涂层,单质Nb固溶到γ-TiAl和α_2-Ti_3Al中,同时形成了新相Ti_3AlNb_(0.3),涂层近似为γ-TiAl+α_2-Ti_3Al双相层片状等轴晶组织。此外,涂层中并未观察到减弱抗氧化性的单质Nb颗粒和Ti_3Al_2相,Ti、Al、Nb的宏观偏析得以消除,涂层与基材界面位置的气孔和裂纹均以消失,出现了明显的白亮带冶金结合过渡层,涂层组织也更加均匀致密。热处理对提高钛合金表面Nb的合金化程度和改善Ti-Al金属间化合物的高温抗氧化性能起到了显著的促进作用。     

Investigate on effect of cryogenic cooling on oxidation wear of WC-Co carbide tool milling titanium alloy

Abstract

For titanium alloy at high cutting speed, the severe tool wear will ineluctably take place diminishing the available tool life because of the high instantaneous temperature rise. Especially the WC-Co material in carbide tool will be reacted with the oxygen element in the air and generate oxide, and the tool oxidation wear is inevitable. In milling Ti–6Al–4V alloy operations, this article presents the first comprehensive investigation on the oxidation wear effect of cryogenic cooling on carbide tool compared with the conventional cooling. Based on the Gibbs free energy of the chemical reaction, the machining characteristics of the oxidation reactions were analyzed in detail. A series of machining testes were executed adopting controllable cryogenic cooling milling system. The surface and cross-section morphology and phase composition characteristics of tool were measured by SEM and XRD measuring equipments, as well as the oxidation wear mechanism of tool in cryogenic cooling. The results show that the thermal oxidation degree of the elements of WC-Co is higher in the conventional cooling processing. After cryogenic cooling intervention, oxidation reactions in tool are reduced significantly. Even the most probable reaction is disappeared, and the oxidation degree is decreased. When the temperature drops to 180 K, it has the best cooling effect. In cryogenic, the effective binding of WC crystal particle to the adhesive phase Co is a major factor for inhabiting oxidation wear of tool. The investigations indicate that the cryogenic cooling method can effectively inhibit the oxidation effect of carbide tool in milling titanium alloy process, and it improves the resist oxidation ability of tool.     

Fretting wear behavior of nitrogen ion implanted titanium alloys in bovine serum lubrication

Nitrogen ion implantation was performed on biomedical titanium alloys by using of the PBII technology to improve the surface mechanical properties for the application of artificial joints. The titanium nitride phase was characterized with X-ray photoelectron spectroscopy (XPS). The nanohardness of the titanium alloys and implanted samples were measured by using of in-situ nano-mechanical testing system (TriboIndenter). Then, the fretting wear of nitrogen ion implanted titanium alloys was done on the universal multifunctional tester (UMT) with ball-on-flat fretting style in bovine serum lubrication. The fretting wear mechanism was investigated with scanning electron microscopy (SEM) and 3D surface profiler. The XPS analysis results indicate that nitrogen diffuses into the titanium alloy and forms a hard TiN layer on the Ti6Al4V alloys. The nanohardness increases from 6.40 to 7.7 GPa at the normal load of 2 mN, which reveals that nitrogen ion implantation is an effective way to enhance the surface hardness of Ti6Al4V. The coefficients of friction for Ti6Al4V alloy in bovine serum are obviously lower than that in dry friction, but the coefficients of friction for nitrogen ion implanted Ti6Al4V alloy in bovine serum are higher than that in dry friction. Fatigue wear controls the fretting failure mechanism of nitrogen ion implanted Ti6Al4V alloy fretting in bovine serum. The testing results in this paper prove that nitrogen ion implantation can effectively increase the fretting wear resistance for Ti6Al4V alloy in dry friction, and has a considerable improvement for Ti6Al4V alloy in bovine serum lubrication.     

Friction surfacing on nonferrous substrates: a feasibility study

This work reports a feasibility study on producing friction surfaced coatings on nonferrous substrates. Commercially pure aluminum, copper, magnesium (ZM21), Inconel 800, and titanium alloy (Ti-6Al-4 V) were chosen as the substrates. Low carbon steel, aluminum alloy (AA6063), commercially pure copper and titanium were chosen as the consumable rods. Friction surfacing was attempted with all consumable rods on every substrate. In some cases metallurgically bonded coating was obtained readily over the substrate and in some other cases coating was obtained with a start-up plate. However, for certain combination of parameters, no coating could be obtained. The coatings obtained were analyzed for their microstructural features and interfacial characteristics using optical and scanning electron microscopy. The results showed that co-efficient of friction, material properties like thermal conductivity, and stability at high temperature influenced the formation of a coating. Coatings obtained exhibited fine grained microstructure with properties better than the original parent material. Dynamic recrystalization as a result of severe plastic deformation accounts for grain refinement.     

Effects of Nd:YAG Laser Surface Treatment on Tribological Properties of Cold-Sprayed Ti-6Al-4V Coatings Tested against 100Cr6 Steel under Dry Condition

The surfaces of cold-sprayed Ti-6Al-4V (Ti64) coatings were laser irradiated with different laser powers of 50–200 W to study the effects of Nd:YAG laser surface treatment on their tribological properties. The hardness of the laser-treated Ti64 coatings became higher with higher laser power due to the more rapid cooling caused by a larger temperature difference between the coating temperature and room temperature. The wear of the laser-treated Ti64 coatings tested against 6-mm 100Cr6 steel balls under dry condition at room temperature decreased with increased laser power as a result of their increased surface wear resistance associated with their increased surface hardness. It could be concluded that the laser surface treatment of the cold-sprayed Ti64 coatings improved their surface wear resistance compared to that of the untreated Ti64 coatings.     

PCBN刀具高速切削钛合金切削力和表面质量的研究

针对PCBN刀具材料和钛合金Ti6Al4V工件材料的特点,采用单因素试验法,对切削力和已加工表面粗糙度进行研究。通过与其它刀具材料作对比,证明了PCBN在高速、低进给量、低背吃刀量下切削钛合金可以得到较平稳的切削力和较低的工件已加工表面粗糙度。     

生物医用钛合金TiN涂层微磨粒磨损及耐蚀性初步研究

对生物医用Ti6Al4V合金表面TiN涂层机械力学性能进行了研究,在分析力学性能的基础上,考察了TiN涂层在蒸馏水和Hank’s模拟体液中的耐磨性,并在Hank’s模拟人体体液中研究了TiN涂层在静态环境中的腐蚀行为。结果表明:在Ti6Al4V合金表面沉积TiN涂层后,其耐磨性和耐蚀性大大提高,有利于改善钛合金在人体环境中的使用寿命。     

Microstructure and Wear Properties of In Situ Synthesized VC Carbide Reinforced Fe-based Surface Composite Coating Produced by Laser Cladding

In situ synthesized VC carbide particles reinforced Fe-based composite coating was fabricated by laser cladding on steel substrate using ferrovanadium (Fe–V) alloy and graphite as the precursor powders. The phase structure and microstructure of the clad layer were investigated by means of X-ray diffraction analysis, scanning electron microscopy, and electron probe microanalysis. Results showed that uniformly distributed VC particles with the radial dendrites shape could be synthesized by the in situ reaction. The hardness and wear properties of the clad coatings were greatly improved due to the presence of VC particles in comparison with the substrate.     

Influence cutting parameters on the surface quality and corrosion behavior of Ti–6Al–4V alloy in synthetic body environment (SBF) using Response Surface Method

Most of the global manufacturing of titanium alloys is related to produce biphasic structures with grains alpha and beta. The development of modern applications of titanium alloy is a great challenge due to the chemical composition of Ti–6Al–4V alloy and the complexity of the manufacturing technology. This study proposed an optimal investigation of the variation of cutting speed, feed rate, and depth of cut in the turning of Ti–6Al–4V alloy on surface roughness, cutting efforts, and corrosion resistance. Response Surface Method has been established to optimize and model the responses mathematically. The adequacy of the models and a significant contribution of parameters were determined by analysis of variance (ANOVA). The biocompatibility of the machined surface for different cutting parameters was evaluated by the electrochemical polarization in simulated body fluids (SBF). Furthermore, desirability function analysis was used to determine the optimal values for surface quality, the turning force, and the passivation rate. It was clearly noticed that the multi-responses of the desirability function improved the machine process. The feed rate and depth of cut were the most relevant factors to minimize surface roughness and the turning forces. Moreover, the experimental results showed that the corrosion behavior was strongly related to minimal surface roughness. Finally, the optimization reduced the surface roughness Ra and Rz in 5.5% and 11.9%, respectively and increased the corrosion resistance in 18.8%.