Transient Thermoelastic Analysis of a Solid Cylinder Containing a Circumferential Crack Using the C–V Heat Conduction Model

This article presents the transient thermoelastic analysis in a long solid cylinder with a circumferential crack using the C–V heat conduction theory. The outer surface of the cylinder is subjected to a sudden temperature change. The Laplace transform technique is adopted to solve the one-dimensional hyperbolic heat conduction equation, and the axial thermal stress is obtained for the un-cracked cylinder in the Laplace domain. Then this axial thermal stress with a minus sign is applied to the crack surface to form a mixed boundary value problem in the cylindrical coordinate system. A singular integral equation is derived by applying the Fourier and Hankel transforms to solve the mode I crack problem. The transient thermal stress intensity factors are obtained by solving the singular integral equation numerically. The influences of thermal relaxation time, crack geometry, and Biot's number upon transient temperature distributions, axial stress fields, and stress intensity factors are analyzed.     

Fe-(Ti,V)C复合材料耐磨性研究

采用原位合成技术制备了碳化钒钛颗粒增强铁基复合材料,采用销盘磨损试验机对复合材料进行了耐磨性试验.采用扫描电镜对该复合材料的微观组织和磨损形貌进行分析.结果表明:随着V含量的增加,Fe-(Ti,V)C复合材料的耐磨性升高,达到最大值后,Fe-(Ti,V)C复合材料的耐磨性又有所下降.     

热氢处理对MIM Ti-6Al-4V组织及性能的影响

系统研究了热氢处理过程中MIMTi-6Al-4V相组成和显微组织的演变规律,尤其是置氢量变化带来的影响,以实现通过热氢处理改善合金力学性能的目的。结果表明,在650℃置氢时,随着置氢量的增加,首先合金中的β相增多,然后开始析出δ相氢化物,并形成越来越多的细小针状组织。在850℃进行固溶和620℃进行等温时效使得合金中的溶氢分布更均匀,δ相的析出更充分,针状组织更加丰富。在720℃进行真空除氢处理后,合金的显微组织保持了细小针状组织的特征,并且置氢量越大时除氢后显微组织的细化效果越显著。置氢量为0.51%(质量分数,下同)时MIMTi-6Al-4V经热氢处理后极限抗拉强度、屈服强度和伸长率分别提高11%、13%和19%。     

Fe83Ga17Tby合金组织结构及磁致伸缩性能

采用Φ7.62 mm装甲钢平头子弹对Ti-6Al-4V合金进行侵彻,分析了Ti-6Al-4V合金弹着点及其弹着点周围宏观与微观组织变化与损伤.结果表明,Ti-6Al-4V合金弹着点微观组织变化与损伤与侵彻不同阶段所受应力、应变、应变硬化、热软化和弹头形状等因素密切相关.在高应变率下,Ti-6Al-4V合金绝热剪切带的形成是一个由萌生、扩展、完全发展组成的过程.Ti-6Al-4V合金弹着点在不同发展阶段的组织变化与损伤不同,各个阶段靶板受力状态在其微观组织变化与损伤中起到非常重要的作用.     

V_8C_7有序-无序相变及衍射消光规律的研究

V8C7有序-无序相变是一类重要的相变。本文通过利用x射线衍射和差热分析研究其相变过程,并计算V8C7、VC0.875衍射消光规律。研究结果表明：V8C7在1200-1300℃之间发生有序一无序相变,相变的温度点为1242℃,（110）、（111）、（210）、（211）、（320）、（421）、（432）晶面产生的衍射超结构线消失。通过对δ-VC1-x和V8C7结构振幅的计算,得到δ-VC1-x衍射消光规律：当h、k、l全为奇数时衍射强度减弱;当h、k、l全为偶数时衍射强度加强;h、k、l为两偶一奇或两奇一偶时完全消光。V8C7衍射消光规律：由于空位有序分布,产生超结构线的晶面为（110）、（111）、（210）、（211）、（320）、（421）、（432）。     

Influence of beam oscillation patterns on the structure and mechanical properties of Ti–6Al–4V electron beam weldments

Abstract

The present study deals with the effect of beam oscillation patterns on the structure and mechanical properties of Ti–6Al–4V electron beam weldments. Electron beam welding of Ti–6Al–4V sheets was done with beam oscillation in various patterns (sinusoidal, square, triangular and elliptical). Welding without beam oscillation was also done for comparison. Room temperature hardness and tensile properties at different temperatures (room temperature, 150, 300 and 450°C) of the weldments in both as welded and post-welding heat treated conditions were observed and their correlations with the microstructure studied. The beam oscillated weldments showed higher ductility and lower strength (hardness) compared with those without being beam oscillated. This was attributed to wider diffusional α plates in the beam oscillated welds owing to slower cooling rates. Elliptical oscillation pattern produced weldments possessing the highest ductility and lowest strength values compared with other oscillation patterns. The oscillating patterns of sinusoidal, square or triangular forms resulted in weldments with almost the same structure and properties.     

Effects of build orientation induced surface modifications on the in vitro biocompatibility of electron beam melted Ti6Al4V

Titanium and its alloys may be processed via additive manufacturing techniques such as electron beam melting (EBM).This field is receiving increased attention from various manufacturing sectors including the medical devices sector. While the economic and engineering potential of EBM for the manufacture of musculo-skeletal implants is clear, the impact on the biocompatibility of the materials has been less investigated. In this study, the effects of part orientation-induced surface modifications on the in vitro biocompatibility of the EBM Ti6Al4V alloy were investigated. The study assessed the suitability of three different Ti6Al4V surfaces produced via the EBM process as variables for proliferation and attachment of mouse fibroblast L929 cells. The three different surface topographies were obtained by orienting the parts in vertical, horizontal and inclined (55°) orientation in the EBM build chamber. The mouse fibroblasts were cultured in vitro on the Ti6Al4V alloy discs with three different surface finishes. Cell viability studies, fluorescent microscopy as well as scanning electron micrographs were used to assess the L929 cell attachment and proliferation. After 2 and 8 days of incubation, there was a higher vitality and proliferation of L929 cells on the vertical and inclined surfaces (R_a?=?38 and 46?µm, respectively) than on the horizontal surfaces (R_a?=?18?µm). On the vertical and inclined samples, the cells spread over a wider area, whereas on the horizontal samples cell spread was affected by the topographical features. The results showed that the implants produced by EBM meet basic biocompatibility requirements and also showed that part orientation of titanium during EBM can produce surfaces with different characteristics and these can affect cell growth.     

Influence of sintering conditions on tensile and high cycle fatigue behaviour of powder injection moulded Ti–6Al–4V at ambient and elevated temperatures

Abstract

Tensile and high cycle fatigue properties of Ti–6Al–4V samples fabricated by powder injection moulding (PIM) are examined at room temperature and elevated temperatures. Standard wrought Ti–6Al–4V material is used for comparison. The tensile and the fatigue strength of samples fabricated by powder injection moulding are found to be significantly lower than conventional wrought material. On the other hand, strength and ductility of metal injection moulded (MIM) samples are high enough to be of large practical interest, in particular if the low processing costs for intricate shapes are taken into account. The inferior properties of the MIM material are caused by considerable remaining porosity, enlarged grain size and increased interstitial content. Prolonged sintering times lead to improved density and strength. At the same time, the room temperature ductility is observed to drop to very low levels, presumably because of additional grain growth.     

Microstructural investigation of as cast and PREP atomised Ti–6Al–4V alloy

Abstract

A microstructure characterisation of Ti–6Al–4V is conducted for cast, extruded and micrometre sized particles. The plasma rotating electrode process is used to produce spherical Ti–6Al–4V powders from an alloy electrode. The process parameters and their impact on the material properties are described. The effects of electrode rotation speed on the particle size distribution, particle shape and crystal structure are investigated in detail. Optical microscopy and scanning electron microscopy are used for microstructural characterisation. The analysis shows that cast and extruded Ti–6Al–4V alloys have equiaxial α and α+β phase structures, while plasma rotating electrode processed powder from the same alloy compositions has an acicular or martensitic (α) structure. The microstructure scale depends on the particle size. Microhardness measurements are used to assess mechanical property dependence on the microstructure of this alloy. The rapidly cooled alloy particles have much higher hardness than cast or extruded bulk alloy.