Ultrasound assisted solidification process of ternary Cu–Sn–Sb alloy

It is well-known that the application of ultrasound during liquid to solid transitions for alloys can refine the solidification microstructure and thus improves the mechanical properties. How-ever, most published work focuses on single phase dendritic growth, whereas little has been con-ducted on the multiphase alloys with complicated phase transformations during solidification. In this work, the solidification process of ternary Cu40Sn45Sb15 alloy was realized within intensive ultra-sonic field with a resonant frequency of 20 kHz and ultrasound power from 0 W to 1000 W. The ultrasound refines the size of the primary e(Cu3Sn) intermetallic compound by two orders of mag-nitudes. If the ultrasound power increases to 1000 W, g(Cu6Sn5) phase nucleates and grows directly from parent liquid phase without the occurrence of peri-eutectic reaction on the top of the alloy sam-ple where the ultrasound intensity is sufficiently high. These microstructural variations lead to the enhancement of compressive strength and elasticity modulus of ternary Cu40Sn45Sb15 alloy.     

Microstructure evolution of a hypereutectic Nb–Ti–Si–Cr–Al–Hf alloy processed by directional solidification

In this work, the Nb–14Si–24Ti–10Cr–2Al–2Hf–0.1Y alloy(at.%) was processed by the liquid–metal-cooled directional solidification(DS) at 1750 C with withdrawal rates of 1.2, 6,18 mm/min and post heat treatment(HT) at 1450 C for 10 h. The microstructures of the directionally solidified and heat treated samples were investigated. The results show that the microstructure of directionally solidified alloy mainly consists of petaloid Nbss+ Nb5Si3eutectics and Ti-rich Nbss+ Nb5Si3+ Cr2Nb eutectics. With the increase of withdrawal rate, the primary Nb5Si3is eliminated, Nbss+ Nb5Si3eutectic cells turn round and connected with the microstructure refinement and Nbss+ Nb5Si3+ Cr2Nb eutectics turn to a river-like morphology. After heat treatment,Nbss+ Nb5Si3+ Cr2Nb eutectics disappeared and petaloid Nbss+ Nb5Si3eutectics turn to a specific fiber-mesh structure gradually, which is promoted by higher withdrawal rates. Furthermore,both the volume fraction of Cr2Nb and the content of Cr in Nbssof Nbss+ Nb5Si3eutectics change regularly with the increase of withdrawal rate and heat treatment at 1450 C for 10 h.     

Selective laser melting of Al–8.5Fe–1.3V–1.7Si alloy: Investigation on the resultant microstructure and hardness

This article presents the microstructure and hardness variation of an Al–8.5Fe–1.3V–1.7Si(wt%, FVS0812) alloy after selective laser melting(SLM) modification. Three zones were distinguished across the melting pool of the SLM-processed FVS0812 alloy: the laser melted zone(LMZ), the melting pool border, and the heat affected zone(HAZ) in the previously deposited area around the melting pool. Inside the LMZ, either an extremely fine cellular-dendritic structure or a mixture zone of the a-Al matrix and nanoscale Al_(12)(Fe,V)_3Si particles appeared. With a decreased laser beam scanning speed, the cellular-dendritic structure zone within the LMZ shrank significantly while the mixture zone expanded. The a-Al and Al_(12)(Fe,V)_3Si mixture zone was also observed in the HAZ, but another phase, submicron h-Al_(13)Fe_4 particles with rectangular or hexagonal shapes,formed along the melting pool border. Microhardness tests indicated that the hardness of the SLM-processed FVS0812 samples far exceeded that of the as-cast FVS0812 alloy.     

Effect of sodium tartrate concentrations on morphology and characteristics of anodic oxide film on titanium alloy Ti–10V–2Fe–3Al

The effect of sodium tartrate concentrations on morphology and characteristics of ano-dic oxide film on titanium alloy was investigated. The alloy substrates were anodized in different concentration solutions of sodium tartrate with the addition of PTFE emulsion and their morphol-ogy and characteristics were analyzed. The anodic oxide film presented a uniform petaloid drums and micro-cracks morphology. Additionally, micro-cracks dramatically swelled with the increase of the tartrate concentrations. The thickness of the anodic oxide film increased with the concentra-tions until the concentration reached 15 g/L. The results of Raman analysis illustrate that all sam-ples have similarity in the crystal structure, consisting of mainly amorphous TiO2, some anatase TiO2 and a small amount of rutile TiO2. And the ratios of anatase TiO2 and rutile TiO2 increase with the concentrations until it reaches 15 g/L. Furthermore, the intensity of the peaks increases with enhanced concentrations until the concentration reaches 15 g/L. The corrosion resistance of the anodic oxide film is increased by the sodium tartrate with higher concentrations before 15 g/L. The coefficient of friction of the anodic oxide film reduces with the concentrations until the concentration reaches 15 g/L, then the coefficient of friction of the anodic oxide film increases with the concentrations.     

Effect of temperature on corrosion behavior of 3003 aluminum alloy in ethylene glycol–water solution

The effect of temperature on the corrosion behavior of 3003 aluminum alloy in ethylene glycol–water solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) techniques. The surface characterization was observed and determined by scanning electron microscopy(SEM), atomic force microscopy(AFM) and energy dispersive spectrometer(EDS). The results demonstrate that the anodic aluminum dissolution and the cathodic oxygen reduction were accelerated by the increased temperature. However, as temperature was over60 °C, the solubility and concentration of oxygen decreased, resulting in the inhibition of cathodic reaction. The cathodic reaction rate of 3003 aluminum alloy rose to the maximum at 60 °C. The Warburg impedance in Nyquist diagram diminished and then was replaced by a negative capacitance caused by the absorption of intermediate corrosion product on electrode. On the other hand,after potentiodynamic measurements, 3003 aluminum alloy suffered pitting corrosion. The dissolution of aluminum alloy around secondary phase particles expanded both horizontally and vertically.     

Tribological evaluation of surface modified H13 tool steel in warm forming of Ti–6Al–4V titanium alloy sheet

The H13 hot-working tool steel is widely used as die material in the warm forming of Ti–6Al–4V titanium alloy sheet. However, under the heating condition, severe friction and lubricating conditions between the H13 tools and Ti–6Al–4V titanium alloy sheet would cause difficulty in guaranteeing forming quality. Surface modification may be used to control the level of friction force, reduce the friction wear and extend the service life of dies. In this paper, four surface modification methods(chromium plating, TiAlN coating, surface polishing and nitriding treatment)were applied to the H13 surfaces. Taking the coefficient of friction(CoF) and the wear degree as evaluation indicators, the high-temperature tribological behavior of the surface modified H13 steel was experimentally investigated under different tribological conditions. The results of this study indicate that the tribological properties of the TiAlN coating under dry friction condition are better than the others for a wide range of temperature(from room temperature to 500 C), while there is little difference of tribological properties between different surface modifications under graphite lubricated condition, and the variation law of CoF with temperature under graphite lubricated is opposite to that under the dry friction.     

Optimization on cooperative feed strategy for radial–axial ring rolling process of Inco718 alloy by RSM and FEM

During radial–axial ring rolling process,cooperative strategy of the radial–axial feed is critical for dimensional accuracy and thermo mechanical parameters distribution of the formed ring.In order to improve the comprehensive quality of the ring parts,response surface method(RSM) is employed for the first time to optimize the cooperative feed strategy for radial–axial ring rolling process by combining it with an improved and verified 3D coupled thermo-mechanical finite element model.The feed trajectory is put forward to describe cooperative relationship of the radial–axial feed and three variables are designed based on the feed trajectory.In order to achieve multiobjective optimization,four responses including thermo mechanical parameters distribution and rolling force are proposed.Based on the FEM results,RSM is used to establish a response model to depict the function relationship between the objective response and design variables.Through this approximate model,effects of different variables on ring rolling process are analyzed connectedly and optimal feed strategy is obtained by resorting to the optimal chart specific to a constraint condition.     

‘Size effect’ related bending formability of thin-walled aluminum alloy tube

Aluminum alloy (Al-alloy) thin-walled (D/t > 20, diameter D, wall thickness t) bent tubes have attracted increasing applications in many industries with mass quantities and diverse specifications due to satisfying high strength to weigh ratio requirements of product manufacturing. However, due to nonlinear nature of bending with coupling effects of multiple factors, the similarity theory seems not applicable and there occurs a challenge for efficient and reliable evaluation of the bending formability of thin-walled tube with various bending specifications. Considering the unequal deformation and three major instabilities, the bending formability of thin-walled Al-alloy tube in changing tube sizes such as D and t are clarified via both the analytical and FE modeling/ simulations. The experiments of rotary draw bending are conducted to validate the theoretical models and further confirm ’size effect’ related bending formability. The major results show that (1) The anti-wrinkling capability of tube decreases with the larger D and smaller t, and the effect significance of t is larger than that of D even under rigid supports; (2) The wall thinning increases with the larger D and smaller t, and this tendency becomes much more obvious under rigid supports; (3) The cross-section deformation increases with the larger D and smaller t according to the analytical model obtained intrinsic relationship, while this tendency becomes opposite due to the nonlinear role of mandrel die; (4) The size factor D/t can be used as a nondimensional index to evaluate both the bending formability regarding the wall thinning and cross-section deformation.     

Improved creep aging response in Al-Cu alloy by applying pre-aging before pre-straining

The improvement of post-form properties without compromising creep formability has been a critical issue in creep age forming of aluminum alloy component. A pretreatment process incorporating artificial pre-aging at 165 °C for 6 h/12 h/24 h followed by pre-strain(3%–9%)has been developed. This method not only evidently improves the strength but also accelerates the creep deformation during creep aging of an Al-Cu alloy. A strength increase of 50 MPa with a slight decrease of ductility relative t...     

氩气保护条件下钎焊单层金刚石砂轮的研究

 利用氩气作为保护气体,以 Ni-Cr合金粉末做钎料,适当控制钎焊温度、保温时间和冷却速度,实现了金刚石与钢基体的牢固的化学冶金结合。利用扫描电镜和 X射线能谱,结合 X射线衍射结构分析,发现在钎焊过程中 Ni-Cr合金中的 Cr元素分离在金刚石界面形成富 Cr层并与金刚石表面的 C元素反应生成Cr₃C₂ 和 Cr₇C₃,在钢基体结合界面上 Ni-Cr合金和钢基体中的元素相互扩散形成冶金结合,这是实现合金层与金刚石及钢基体之间都有较高结合强度的主要因素。并通过重负荷磨削实验进行验证取得较好的结果。     

钛合金高温钎焊接头的组织性能及影响因素评价

综述了钛及钛合金高温钎焊结构在现代工业中的应用。在分析了钛基钎料应用和发展的基础上，重点分析了钎焊接头的组织与接头性能的关系以及影响因素。指明接头组织中脆性金属间化合物相的存在形态是决定接头性能的主要因素，接头间隙和钎焊时间决定了接头的组织形态，从而影响接头的性能。钛及钛合金高温钎焊接头的拉伸性能、高温性能和疲劳性能是优越的，而接头氧化后的性能急剧下降。并展望了钛基材料连接的发展方向。     

BNi-2非晶钎料钎焊高铌TiAl合金与GH3536合金接头组织与性能

采用非晶态BNi-2钎料成功实现了高铌TiAl合金与GH3536合金的连接,获得良好的钎焊接头。钎焊接头的典型界面组织为TAN/B2+τ3/τ4+（Ni-Ti）-B/γ+（Ni-Ti）-B+CrB+G相/GH3536。通过分析钎焊温度对接头界面微观组织的影响,表明BNi-2钎料中B元素的扩散以及GH3536合金向液态钎料中的溶解对界面组织结构演变起着至关重要的作用。而随着钎焊温度的升高,扩散IV区逐渐消失,接头由4个区域变为3个区域,τ3/τ4化合物层及钎缝区域均逐渐增厚,黑色CrB相发生粗化,细小点状（Ni,Ti）-B含量减少。1 160℃保温10 min时,所获得的钎焊接头最大室温及高温（700℃）抗剪强度分别为~106.8 MPa和~76.2 MPa,其剪切强度降低约28.6%,接头均呈现脆性断裂模式。接头形成过程可以划分为固相扩散、液相生成、等温扩散凝固和残余液相析出4个阶段。     

TiAl合金与40Cr钢的真空钎焊研究

采用Ag-Cu-Ti钎料进行了TiAl合金与40Cr钢的真空钎焊连接,用拉伸试验对接头的连接强度进行检验,采用扫描电镜、电子探针和X-射线衍射分析等手段对接头断口的形貌、界面原子扩散、界面反应及界面产物进行了分析.研究结果表明,采用Ag-Cu-Ti钎料时得到的焊缝具有很高的强度(426MPa),是因为钎料和TiAl母材中的Ag,Cu,Ti原子发生了互扩散,而且在钎料与母材的界面发生了界面反应,形成了AlCu2Ti相,实现了冶金上的结合.     

C_f/SiC复合材料与Ti合金的AgCuTi-W复合钎焊

本文利用AgCuTi-W复合钎料作中间层,在适当的工艺参数下真空钎焊Cf／SiC复合材料与Ti合金,利用SEM,EDS,XRD分析接头微观组织结构,利用剪切试验检测接头力学性能。研究结果表明：钎焊时,复合钎料中的Ti借助Cu-Ti液相与Cf／SiC复合材料反应,在Cf／SiC复合材料与连接层界面形成Ti3SiC2,Ti3Si和少量TiC化合物的混合反应层。复合钎料中的Cu与Ti合金中的Ti发生互扩散,在连接层与Ti合金界面形成不同成分的Cu—Ti化合物过渡层。钎焊后,形成W颗粒强化的致密复合连接层,W颗粒主要分布在Cu-Ti相中。W的加入缓解了接头的残余热应力,Cf／SiC／AgCuTi—W／TC4接头剪切强度明显高于CF／SiC／AgCuTi／TC4接头。     

DZ125合金钎焊接头窄钎缝区高温循环应力应变分析方法

针对钎焊接头窄钎缝区(大约150μm)在高温环境下的循环应力应变测量困难问题,提出一种基于反推法的新思想,依据以下两类数据进行计算和分析:第一类是采用有限元软件ABAQUS的用户材料子程序(UMAT)嵌入Chaboche热黏塑性本构模型计算得到的DZ125母材合金高温循环应力应变数据;第二类是经高温循环试验得到的钎焊接头的相应数据,最后经过数据处理和MATLAB软件编程获得窄钎缝区的应力应变.研究结果表明,钎焊接头在高温环境下的变形具有明显的不均匀性和局部性,并指出较之母材合金其钎缝区相对较“软”,而且它也是整个钎焊接头的薄弱环节,应给予足够的重视.推而广之,反推法的提出为研究普通焊接接头窄焊缝的力学行为提供了一条新的途径.      

钴对钛基钎料钎焊Ti3Al的影响

研究了Co的添加对Ti-Zr-Ni-Cu钎料的性能,以及对Ti3Al基合金钎焊接头的显微组织和机械性能的影响。研究结果表明:采用添加Co的钎料,具有良好的润湿性和流动性,可显著提高钎焊接头的拉伸强度。     

真空加压钎焊FGH96/DD6接头的组织和性能

采用Ni-Cr-B钎料分别在1120℃/10 min和1120℃/10 min/2 MPa的工艺下实现FGH96与DD6的钎焊连接。测试两种工艺下接头的抗拉强度,通过光学显微镜(OM)、扫描电子显微镜(SEM)和电子探针(EPMA)分析接头的组织、成分和断口。结果表明:真空加压钎焊所得接头的室温平均抗拉强度达到1187 MPa,远高于真空钎焊接头621 MPa的强度;与不加压的真空钎焊相比,真空加压钎焊所得FGH96/DD6接头的钎缝中心没有平行于被焊面的晶界,而是单个晶粒贯穿整个钎缝,并与母材连接面发生韧性断裂;真空钎焊接头中存在Ni3B相,而真空加压钎焊钎缝中并没有残留的Ni3B相,主要由(Ni,Cr)固溶体组成。     

Investigation on induction brazing of profiled cBN wheel for grinding of Ti-6Al-4V

Profiled monolayer cBN wheel was induction brazed for grinding of titanium dovetail slot in this study. Aimed at acquiring a uniform temperature distribution along the profiled surface and reducing the thermal deformation of the brazed wheel, a finite element model was established to investigate the temperature uniformity during induction brazing. A suitable induction coil and the related working parameters were designed and chosen based on the simulation results. Ag-Cu-Ti alloy and cBN grains were applied in the induction brazing experiment. The results showed geometric deformation of the brazed wheel was no more than 0.01 mm and chemical reaction layer were found on the brazed joint interface. Further validation tests were carried out by grinding of Ti-6Al-4V alloy. Compared to the electroplated wheel, the brazed wheel showed better performance such as low specific grinding energy and good ground quality in grinding of Ti-6Al-4V alloy. Abrasion wear was found to be the main failure mode for the induction brazed wheel, while adhesion and grains pull-out were the main failure mode for the electroplated wheel.     

钴基钎料钎焊K465合金大间隙接头组织与性能

采用Co45Ni Cr WB钴基钎料,预填FGH95镍基合金粉,在1220℃不同保温时间下对K465高温合金进行0.5 mm大间隙真空钎焊实验,研究钎缝组织构成及不同保温时间对钎缝组织与接头性能的影响。结果表明:钎缝组织由合金粉颗粒及颗粒间硼化物相构成,颗粒内为γ和γ'双相组织和少量小块状硼化相,颗粒间是高Cr,W和Nb的硼化物相;钎焊时随保温时间延长合金粉长大,化合物相合并长大;合金粉比例高、保温时间适当获得钎缝中化合物相细小弥散分布,对接头性能有利;钎焊保温30~60 min时接头持久性能较高。