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.     

Characterization of LENS-fabricated Ti6Al4V and Ti6Al4V/TiC dual-material transition joints

The design of engineering structures with function-specific material members is on the increase. This requires advanced fabrication technologies with capabilities for multi-material processing. A major challenge however is obtaining effective transition from one material to another. Dissimilar material systems made using laser metal deposition processes have been investigated. The fusion of materials having different physical properties and chemical compositions under high laser power often results in defects at the joints due to thermal expansion mismatch, the formation of intermetallics, or other mechanisms. Some solutions have been proffered in previous works based on evaluations using qualitative techniques. However, quantitative experimental studies are imperative to accurately assess the mechanical behavior of dual-material structures for real-life applications as predictive tools have not yet been validated. In this work, different designs of material transitions from Ti6Al4V alloy to Ti6Al4V/TiC composites were established. Experimental evaluations of their strengths at these joints were made using LENS-fabricated tensile and flexural test samples. The mode of transition from one material to another was found to have a significant effect on the tensile strengths of the structures. Also, material transition designs with optimum strengths were applied for the fabrication of simplified dual-material minimum-weight structures and tested. The structures failed at locations away from the material transition regions, thus proving the effectiveness of the joints.     

超声振动铣削加工Ti6Al4V的表面残余应力研究

建立了包含振动铣削、移除铣刀、载荷释放及降温等多个分析步的超声振动铣削三维有限元模型,对铣削表面的残余应力进行了仿真。通过有限元计算,得到了不同振动参数和铣削用量条件下加工表面的残余应力大小与分布情况,并根据振动切削表面残余应力的影响机制对仿真结果进行了分析。研究结果表明,对工件施加超声振动后,切削表面残余拉应力值明显减小;振动参数和铣削速度对残余应力的影响较大,而进给量对残余应力的影响较小,并通过相关实验验证了有限元仿真结果的正确性。     

Enhancement of surface roughness in electrochemical machining of Ti6Al4V by pulsating electrolyte

Electrochemical machining (ECM) is widely used in machining a variety of components used in aerospace, defence, automotive and medical applications. The surface roughness of the ECM process has become important because of increased quality demands. Considerable attention has been paid to achieving low surface roughness in ECM. Surface roughness is closely related to the distribution of gases and Joule heat produced during the ECM process, which affect the electrolyte electric conductivity and directly determine the surface roughness. In this report, a pulsating electrolyte, which is one of the unsteady flows that are characterized by periodic fluctuations of the mass flow rate and pressure, is first introduced to the ECM process. The ECM process is affected by the pulsating electrolyte because it can modify the heat transfer. The goal of this report is to present experimental results of the surface roughness obtained on Ti6Al4V samples using a developed pulsating electrolyte supply system in ECM. It is observed that a lower surface roughness and higher material removal rate could be obtained by using a pulsating electrolyte with proper pulsating frequency and amplitude. In direct current ECM, the surface roughness Ra is 5.7 μm, the material removal rate is 0.85 g/min at a constant electrolyte, the lowest surface roughness is 3.69 μm and the largest material removal rate is 0.92 g/min, which are obtained at a pulsating frequency of 10 Hz and amplitude of 0.2 MPa. In pulsed current ECM, the surface roughness Ra and material removal rate are 0.67 μm and 0.38 g/min at a constant electrolyte, respectively, and both the minimum surface roughness Ra of 0.53 μm and maximum material removal rate of 0.39 g/min are observed when the proper pulsating electrolyte flow frequency and amplitude are used.     

Tribocorrosion of Diamond-Like Carbon Deposited on Ti6Al4V

Tribological and corrosion properties of Ti6Al4V alloy both bare and coated by diamond-like carbon (DLC) were investigated in PBS solution. The films obtained by a PACVD technique present high hardness, good corrosion and wear resistance and lower friction coefficient compared to bare alloy. Tribocorrosion tests on bare alloy showed that when wear stops, the alloy rapidly passivates. DLC films present superior wear resistance under dry conditions. However, film life is greatly reduced during tribocorrosion tests. An erratum to this article can be found at     

Solid particle erosion behaviour of Ti6Al4V alloy

Abstract

The effects of particle impingement angle, impingement velocity and erodent particle size on the erosion rate and surface morphology of the Ti6Al4V alloy have been investigated comprehensively in order to evaluate solid particle erosion behaviour of Ti6Al4V alloy. Samples were eroded in a specially designed sandblasting system under various parameters using alumina (Al₂O₃) erodent particles. Surface morphology investigations were examined by scanning electron microscope using various analysis and modes (energy dispersive X-ray analysis, elemental mapping and compositional contrast). Ti6Al4V alloy showed ductile behaviour with a maximum erosion rate at 30° impingement angle. Erosion rate of Ti6Al4V alloy increased with increases in velocity and decreased with increases in erodent particle size. Scanning electron microscopy investigations of eroded surfaces of Ti6Al4V alloy samples reveal the dominant erosion mechanism such as microploughing, microcutting and plastic deformation. Embedded erodent particles on the surfaces of Ti6Al4V alloy nearly at all particle impingement angles and velocities were clearly detected.     

钛合金Ti6Al4V铣削力试验分析

对钛合金Ti6Al4V进行了铣削试验,测量了铣削过程中的切削力.利用最小二乘法对试验数据进行回归分析,建立了切削力的经验模型,得出了切削参数对切削力的影响规律,为优化切削参数、研究切削机理提供了参考依据.     

The effects of cooling conditions on surface integrity in machining of Ti6Al4V alloy

This paper presents results from a comparative study of machining of Ti6Al4V alloy under dry, minimal quality lubrication, and cryogenic cooling conditions using coated tools at varying cutting speeds and feed rates. The influence of the cooling conditions on surface integrity and the product performance was studied in terms of surface roughness, metallurgical conditions, including microstructure, hardness, grain refinement, and phase transformation of the machined product. Results show that cooling conditions affect surface integrity of the product signifying the benefits of cryogenic cooling in improving the overall product performance.     

Investigation of the correlation between mechanical chip morphology and surface residual stress for Ti6Al4V alloy

Journal of Mechanical Science and Technology - A numerical simulation analysis of mechanical chip morphology and residual stress for Ti6Al4V alloy was conducted under different cutting speed and...     

置氢钛合金切削变形的实验研究

进行了爆炸落刀实验获取不同置氢量钛合金TC4的切屑根部,通过对切屑根部各变形区和切屑形态的分析研究置氢量影响钛合金切屑变形的规律.分析发现,置氢后钛合金的各变形区的变形量减小了,切屑由明显的锯齿形转变为近似带状的切屑.进一步测量了置氢钛合金切削过程中的切削力和切削温度,并根据切削变形量的减小解释了切削力和切削温度降低的机理.     

Slurry abrasion response of surface engineered Ti6Al4VELI

Titanium alloys, by virtue of their outstanding combination of properties, continue to evolve as direct replacements for steels in offshore production systems to meet the challenging offshore application conditions. However, the wider use of titanium and its alloys is frequently retarded by their reputation for poor tribological behaviour. It is because of this simple engineering scenario that comparative tribological behaviour of surface engineered Ti6Al4VELI in abrasive slurry has been evaluated to identify treatments capable of improving its wear behaviour. To best simulate potential application conditions, sliding wear tests were carried out using a block-on-wheel test configuration in abrasive mud slurry. The wear volumes lost from the surface engineered Ti6Al4VELI test blocks ranged from negligibly small for substrates plasma sprayed with either WC–Co, Ni–Cr or Mo, to approximately twice that measured for a steel test block in the cases of untreated, shot peened, electroless Ni plated and anodised Ti6Al4VELI. Hard chrome plated material and thermochemically treated material demonstrated a certain degree of wear, which however, was significantly less than that found for the steel block.     

Ti6Al4V表面生物活性陶瓷涂层的摩擦学性能

人工合成的生物活性陶瓷被广泛应用于金属内植入体表面用以修复或置换缺损的骨组织。使用自制的往复试验机,在6.5 mm/s的滑动速度和不同载荷(1 N和2 N)下对溶胶-凝胶法制备的生物活性陶瓷羟基磷灰石(HAP∶Ca10(PO4)6(OH)2)和二氧化钛涂层,以及羟基磷灰石/二氧化钛复合涂层进行了摩擦学性能的研究。结果显示,由不同工艺路线制备的HAP涂层的抗磨性有一定的差异,其中采用有机磷酯前驱体法制备的HAP涂层的抗磨性较好,但它们的抗磨性均差于二氧化钛涂层;羟基磷灰石/二氧化钛复合涂层的抗磨性与两者的复合方式有关,其中非晶态结构的复合涂层的抗磨性最佳。     

钛合金Ti6Al4V高速磨削试验研究

为实现难加工材料钛合金的高效磨削,进一步发挥高速磨削的潜力,开展了钛合金Ti6Al4V高速磨削工艺试验研究,对磨削过程的磨削力、磨削比能以及磨削温度随单颗磨粒最大切屑厚度agmax的变化特征进行了分析。研究结果表明：不同砂轮线速度vs条件下,磨削力、磨削比能及磨削温度三者随单颗磨粒最大切屑厚度agmax变化的特征曲线略有不同,具体表现为,单颗磨粒最大切屑厚度agmax一定条件下,磨削力及磨削比能随着磨削速度的提高呈减小趋势,磨削温度则呈上升趋势,同时钎焊CBN砂轮的磨削力、磨削比能低于陶瓷结合剂及电镀CBN砂轮的磨削力、磨削比能,因此,利用钎焊CBN砂轮磨料有序排布的优势,选择合理的单颗磨粒最大切屑厚度,可在提高砂轮线速度的同时提高进给速度,从而提高磨削效率,实现钛合金的高速高效磨削。     

Ti6Al4V的微磨粒磨损研究

研究了医用Ti6Al4V合金在蒸馏水中的微磨粒磨损行为,考察了载荷、滑行距离、料浆浓度和转速对微磨粒磨损规律的影响,并对微磨粒磨损机制进行了讨论。结果表明:随载荷、滑行距离和料浆浓度的增加,Ti6Al4V合金的磨损量增加,磨损机制由三体磨损转变为混合磨损。     

Effect of laser power on the microstructure and mechanical properties of TiN/Ti3Al composite coatings on Ti6Al4V

Laser nitriding is one of the effective techniques to improve the surface properties of titanium alloys and has potential application in the life extension of last-stage steam turbine blades. However, cracking of surface coating is a common problem due to heat concentration in laser nitriding process. Conventionally, the cracks can be avoided through heat treatment, which may have an important influence on the mechanical properties of coating. Crack-free TiN/Ti3Al IMC coatings on Ti6Al4V are prepared by plasma spraying and laser nitriding. The microstructures, phase constitutes and compositions of the coating are observed and analyzed with scanning electron microscopy(SEM), X-ray diffraction(XRD) and X-ray energy-dispersive spectroscopy(EDS). Microhardness, elastic modulus, fracture toughness of the coating are measured. The results show that the crackand pore-free IMC coatings can be made through the proposed method; with increasing laser power, the amount and density of TiN phase in the coating first increased and then decreased, leading to the similar trend of microhardness and elastic modulus and the reverse trend of fracture toughness of the coating. Both the average microhardness and elastic modulus of the coating increase three times higher than those of the substrate. The volume fraction of the TiN reinforced phase in composite can be controlled by varying the laser power and the cracking problem in laser nitriding process is successfully solved.     

Ti6Al4V/WC-Co干摩擦性能研究

利用Optimal SRV高温摩擦磨损试验机,研究干摩擦条件下钛合金(Ti6Al4V)对硬质合金(WC-Co)的摩擦学性能.研究了载荷、温度与滑动速度对摩擦过程的影响,通过磨损区微观形貌表征分析了磨损机理.结果表明:Ti6Al4V与WC-Co的摩擦系数波动剧烈,产生了严重的黏滑摩擦,且随着载荷、温度与滑动速度的增加,黏...     

Adaptive fuzzy sliding-mode control for the Ti6Al4V laser alloying process

It is well known that surface alloying quality may vary significantly with respect to process parameter variation. Thus a feedback control system is required to monitor the operating parameters for yielding a good quality control. Since this multi-input and multi-output (MIMO) system has nonlinear coupling and time-varying dynamic characteristics, it is very difficult to establish an accurate process model for designing a model-based controller. Hence an adaptive fuzzy sliding-mode controller (AFSMC) which combines an adaptive rule with fuzzy and sliding-mode control is employed in this study. It has an on-line learning ability for responding to a system’s nonlinear and time-varying behaviours. Two adaptive fuzzy sliding-mode controllers are designed for tuning the laser power and the traverse velocity simultaneously to tackle the absorptivitiy and geometrical variations of the work pieces. The simulation results show that good surface lapping performance is achieved by using this intelligent control strategy.     

3D FEM simulation of milling process for titanium alloy Ti6Al4V

Milling is used as one of the most important tools with the complex tool geometry in industry. However, the complex milling process cannot be simulated by 2D finite element method. Therefore, a more real 3D finite element model (FEM) for the complex milling process of titanium alloy Ti6Al4V is firstly developed using the finite element software ABAQUS. This model takes into account the dynamic effects, thermomechanical coupling, material damage law, and contact criterion. Firstly, the Johnson–Cook material constitutive equation was proposed, considering the effects of strain, strain rate, and temperature on material properties. Secondly, the damage constitutive law was adopted as the chip separation criterion. Then, the simulation for the milling process of Ti6Al4V was conducted through ABAQUS based on the established 3D FEM. Finally, chip formation, stress distribution, cutting force, and milling temperature were obtained. Further, a series of milling experiments of Ti6Al4V were carried out to validate the simulation results. It confirms the capability and advantage of 3D FEM simulation in the complex milling process of titanium alloy.