钛合金纳秒激光打孔数值模拟和实验研究

为了描述纳秒激光对钛合金打孔过程中孔的形貌及温度场的变化规律,建立激光打孔的物理模型,利用ANSYS中APDL语言进行编程,对温度场进行仿真分析,并利用单元生死技术模拟孔形貌的变化过程。从有限元数值模拟和实验两方面综合分析比较了激光工艺参数(脉冲能量和脉冲数量)对打孔质量(孔深和孔径)的影响,系统论述了钛合金纳秒激光打孔的一般规律,以达到工艺参数优化,提高打孔质量的目的。     

倾斜表面的纳秒激光抛光研究

考察倾斜表面纳秒激光抛光后的表面形貌演化规律及表面倾斜程度对抛光效果的影响规律,可以为增材制造中的自由曲面激光抛光提供参考。采用纳秒激光对不垂直于光轴的粗糙平面进行激光抛光,并采用激光共聚焦显微镜对激光抛光后的表面形貌进行测试分析。结果表明：表面倾斜30°时,抛光后的表面在距离起始点4 mm附近存在表面轮廓波动异常增大的现象,表面粗糙度值增大到15.80μm;倾斜角度增大到45°时,表面轮廓波动异常增大的位置变化到2 mm附近;倾斜角度为60°时,未发生表面轮廓波动异常增大现象。表面轮廓波动异常增大现象反映了激光抛光从过熔型抛光到浅熔型抛光的过渡过程;自由曲面的激光抛光工艺需要根据抛光区域的倾斜程度和表面粗糙度选定合适激光功率密度和离焦量,从而实现良好的激光抛光质量。     

双步激光辐射提升纳秒激光抛光单晶硅的表面

单晶硅是一种重要的半导体材料。通常,铸锭切片后的单晶硅表面易产生较深的沟槽、凹坑和裂纹等缺陷。针对这一问题,提出了一种双步激光辐射的方法,其在修复表面缺陷的同时,可以降低表面粗糙度。首先,通过有限元法模拟对不同激光参数下可修复的缺陷深度进行预测。然后,在0.50 J/cm²的较高能量密度下,利用较深的表面层熔化修复各种深度的表面缺陷。然而,由于高能量密度下引发的热毛细管流易造成高频特征残留在表面上,故会导致表面粗糙度增加。接着,使用一个0.20 J/cm²的低能量密度再次辐射同一表面,可有效消除残留的高频特征。最终,原始表面粗糙度为1.057μm的表面经过双步激光辐射后可获得一个表面粗糙度为26 nm的无缺陷光滑表面。     

Ti6Al4V合金表面激光沉积复合涂层的组织和性能

为了增强Ti6Al4V钛合金的耐磨性,采用激光沉积制造方法在其表面上制备了以原位生成的TiC颗粒和直接添加的WC颗粒为增强相的耐磨涂层,观察了各涂层的微观组织,并测量了涂层的显微硬度和涂层在室温大气条件下的摩擦磨损性能。结果表明各涂层和基体呈现冶金结合,原位自生的TiC和部分熔化的WC颗粒均能够均匀弥散分布于基体上,由于增强相颗粒的弥散强化及激光沉积组织的细晶强化作用,基材的硬度和耐磨性均得到了提高。原位自生的TiC涂层比WC涂层硬度梯度分布平缓,但耐磨性稍差。     

磁流变抛光工艺参数的正交实验分析

对利用自行配制的水基磁流变抛光液和磁流变抛光实验样机进行了以抛光去除效率和表面粗糙度为考核指标的工艺实验。应用正交试验方法分析了磁流变抛光中主要工艺参数(磁场强度、抛光粉浓度、抛光盘的转速、抛光盘与工件间的间隙)对抛光去除效率和表面粗糙度的影响规律,并结合磁流变抛光机理对其进行了分析。根据实验结果对工艺参数进行了优化。     

纳秒激光脉冲诱导硅表面微结构

利用Nd:YAG纳秒激光脉冲,在能量密度为1～10 J/cm2范围内辐照单晶硅,形成了表面锥形微结构,在SF6气氛和空气环境下均形成了锥形尖峰表面微结构。SF6气氛下产生的锥形尖峰顶端都有小球,部分锥形上还有二次尖峰形成,空气中纳秒激光诱导的锥形尖峰微结构顶端和边缘有由液滴固化形成的粒状物质,不同于利用准分子纳秒激光诱导的细长须状结构和飞秒激光辐照下产生的具有表面枝蔓状纳米结构的锥形微结构。实验结果表明,这种尖峰微结构的形成与辐照激光的波长和脉冲持续时间有关。对空气中微构造硅的辐射反射的初步研究表明,在500～2 400 nm范围内的光辐射反射率不高于20%。     

纳秒激光脉冲诱导硅表面微结构

利用Nd:YAG纳秒激光脉冲,在能量密度为1~10 J/cm2范围内辐照单晶硅,形成了表面锥形微结构,在SF6气氛和空气环境下均形成了锥形尖峰表面微结构。SF6气氛下产生的锥形尖峰顶端都有小球,部分锥形上还有二次尖峰形成,空气中纳秒激光诱导的锥形尖峰微结构顶端和边缘有由液滴固化形成的粒状物质,不同于利用准分子纳秒激光诱导的细长须状结构和飞秒激光辐照下产生的具有表面枝蔓状纳米结构的锥形微结构。实验结果表明,这种尖峰微结构的形成与辐照激光的波长和脉冲持续时间有关。对空气中微构造硅的辐射反射的初步研究表明,在500~2 400 nm范围内的光辐射反射率不高于20 %。     

纳秒激光烧蚀下液态金属表面微结构的形成

首次发现了在不同保护气体及多脉冲uV—IR激光的照射下,液态金属的微型突起和微结构的形成。测量表明,针对不同的金属和保护气,这种结构的单脉冲生成速率可达（5—20）μm／pulse,形成了长度为1～2mm,直径约为焦点两倍的单个微型突起。最后,介绍了控制微结构形状的可能性,并讨论了它们的应用潜力。     

Nd:YAG纳秒激光诱导硅表面微结构的演化

利用Nd:YAG纳秒激光(波长为532和355 nm)对单晶硅在真空中进行了累积脉冲辐照,研究了表面微结构的演化情况.在激光辐照的初始阶段,532和355 nm激光脉冲均在硅表面诱导出了波纹结构,后者辐照硅表面后形成了近似同心但稍显混乱的环形波纹结构.随着脉冲数的增加,波纹结构逐渐演化为一种类似珠形的凹凸结构,最后形成准规则排列的微米量级锥形结构,该微结构的生长依赖于表面张力波和结构自组织.分析发现,形成的交叉环形结构主要是在355 nm激光辐照硅的过程中,表面张力波导致波纹结构部分叠加的结果.     

气囊抛光工艺参数的正交实验分析

针对平面光学零件,以抛光去除率和表面粗糙度为考核指标,应用正交试验法分析了气囊抛光过程中的主要工艺参数,包括抛光工具气囊的压缩量、气囊转速、气囊内部充气压力、抛光液的浓度对抛光去除效率和表面粗糙度的影响规律。结合气囊抛光的抛光机理对其进行了分析,根据实验结果对工艺参数进行了优化,并进行了综合参数的气囊抛光加工实验,获得了超精密光滑的表面。     

Surface ablation by excimer laser irradiation of Ti and Ti6Al4V alloy

This paper presents the surface microstructure of Ti and Ti6Al4V alloy irradiated with a high output energy XeCl ( = 308 nm) excimer laser. The treatments are carried out on both materials at two beam fluences and the effects of single- and multiple-pulse irradiation are compared. The results of the scanning electron microscopy and of the X-ray diffraction techniques suggest the possible influence of both time-behaviour and energy fluence of the laser pulse on the relative weight of the ablation rate and of the reaction product deposition rate at the sample surface.     

Enhanced fatigue performance of porous coated Ti6Al4V biomedical alloy

Biofunctional coatings are necessary to improve integration of titanium implants in the host tissue but they may be detrimental for the implant fatigue properties. This study presents an attempt towards enhancement of the in vitro fatigue strength of plasma electrolytic oxidation coated Ti6Al4V alloy by applying shot peening process prior to coating. The electrolytic oxidation was performed in calcium acetate and calcium glycerophosphate electrolytes that allowed formation of porous oxide coatings with high surface free energy and apatite like ability. A deformed surface layer coupled with induced residual compressive stresses seem to affect oxide growth rate and fatigue behavior of the titanium alloy.     

Reactive resistance welding of Ti6Al4V alloy with the use of Ni(V)/Al multilayers

The freestanding Ni(V)/Al multilayer foil was applied as a filler material in order to join Ti6Al4V alloy with the use of reactive resistance welding (RRW) technique. Present investigations, performed with the use of transmission electron microscopy (TEM) method, allowed to show that an application of high current (I = 400 A for 2 min in vacuum conditions ～10^–1 mbar) transformed the Ni(V)/Al multilayers into fine grain (<300 nm) NiAl phase. It also showed that the RRW process led to the formation of firm connection with nanoporosity limited only to the original contact plane between base material and the foil. Simultaneously, the formation of a narrow strip of crystallites of Ti₃Al intermetallic phase elongated along the joint line (average size of ～200 nm) was observed. The base material was separated from the joint area by a layer of up to ～2 μm thickness of nearly defect free α‐Ti and β‐Ti grains from a heat affected zone (HAZ). The performed experiment proved that Ni(V)/Al multilayer could serve as a filler material for joining of Ti6Al4V alloys even without additional solder layer. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Numerical and experimental study of the Ti6Al4V macrostructure obtained by Nd:YAG laser

Titanium and its alloys (Ti6Al4V) have been widely used in the biomedical field; nevertheless, they should be subject to specific surface treatments, before being implanted, in order to improve bio-integration. Although laser processing is a useful technique for this purpose, different aspects of the basic mechanisms of this process are still in progress, with special emphasis on the modeling structure formation on the irradiated surface. For this research, the finite element method was used to study the generation of a macrostructure on the Ti6Al4V surface using a Nd:YAG laser. The temperature profiles, estimated during the extremely high heating and cooling rates caused by the output power of the laser beam, allowed us to analyze, among other things, the melting depth and the heat affected zone, in order to optimize the process. Moreover, the experimental results (SEM data) were positively compared with the numerical model, and a relationship of the crater profile formation (depth to width ratio) was determined.     

Effect of micro-particles on cavitation erosion of Ti6Al4V alloy in sulfuric acid solution

The influences of micro-particles on ultrasonic cavitation erosion of Ti6Al4V alloy in 0.1 M H₂SO₄ solution were investigated using mass loss weight, scanning electron microscopy (SEM) and white light interferometer. Mass loss results revealed that the cavitation erosion damage obviously decreased with increasing particle size and mass concentration. Open circuit potential recorded during cavitation erosion shifted to positive direction with the decreased mass loss. Meanwhile, the mass loss sharply decreased with applying a positive potential during the entire ultrasonic cavitation erosion, and the relationship between the open circuit potential and the cavitation erosion resistance was discussed.     

Microstructure and tribological behaviors of Ti6Al4V alloy treated by plasma Ni alloying

Ni modified layer was prepared on surface of the Ti6Al4V substrate by plasma surface alloying technique. Surface morphology, micro-structure, composition distribution, phase structure, and microhardness of the Ni modified layer were analyzed. Tribological performance of the Ni modified layer and Ti6Al4V substrate was investigated by using pin-on-disc tribometer. The results indicate that roughness of the Ni modified layer was increased due to formation of the micro-convex on the modified surface. The concentration of Ni gradually decreased from the surface to interior. The maximum content of Ni atoms was nearly 90%. The modified layer was composed of TiNi, Ti2Ni and Ti phases. The maximum microhardness of the Ni modified layer was about 677 HV_0.025 which was increased about two-fold of microhardness of the control Ti6Al4V substrate. Wear resistance of the Ni modified layer was improved obviously, and showed micro-abrasion wearing. The strengthened mechanism of the as-treated Ti6Al4V alloy is discussed.     

Fixation of bioactive calcium alkali phosphate on Ti6Al4V implant material with femtosecond laser pulses

Bone implants made of metal, often titanium or the titanium alloy Ti6Al4V, need to be surface treated to become bioactive. This enables the formation of a firm and durable connection of the prosthesis with the living bone. We present a new method to uniformly cover Ti6Al4V with a thin layer of ceramics that imitates bone material. These calcium alkali phosphates, called GB14 and Ca10, are applied to the metal by dip coating of metal plates into an aqueous slurry containing the fine ceramic powder. The dried samples are illuminated with the 790 nm radiation of a pulsed femtosecond laser. If the laser fluence is set to a value just below the ablation threshold of the ceramic (ca. 0.4 J/cm²) the 30 fs laser pulses penetrate the partly transparent ceramic layer of 20-40 μm thickness. The remaining laser fluence at the ceramic-metal interface is still high enough to generate a thin metal melt layer leading to the ceramic fixation on the metal. The laser processing step is only possible because Ti6Al4V has a lower ablation threshold (between 0.1 and 0.15 J/cm²) than the ceramic material. After laser treatment in a fluence range between 0.1 and 0.4 J/cm², only the particles in contact with the metal withstand a post-laser treatment (ultrasonic cleaning). The non-irradiated rest of the layer is washed off. In this work, we present results of a successful ceramic fixation extending over larger areas. This is fundamental for future applications of arbitrarily shaped implants.     

Structure and tribological performance by nitrogen and oxygen plasma based ion implantation on Ti6Al4V alloy

Ti6Al4V alloy was implanted with nitrogen-oxygen mixture by using plasma based ion implantation (PBII) at pulsed voltage −10, −30 and −50 kV. The implantation was up to 6 × 10¹⁷ ions/cm² fluence. The changes in chemical composition, structure and hardness of the modified surfaces were studied by XPS and nanoindentation measurements. According to XPS, it was found that the modified layer was predominantly TiO₂, but contained small amounts of TiO, Ti₂O₃, TiN and Al₂O₃ between the outmost layer and metallic substrate. Surface hardness and wear resistance of the samples increased significantly after PBII treatment, the wear rate of the sample implanted N₂-O₂ mixture at −50 kV decreased eight times than the untreated one. The sample implanted N₂-O₂ mixture showed better wear resistance than that of the sample only implanted oxygen at − 50 kV. The wear mechanism of untreated sample was abrasive-dominated and adhesive, and the wear scar of the sample implanted at −50 kV was characterized by abrasive wear-type ploughing.