Thermal analysis of laser surface transformation hardening—optimization of process parameters

This paper deals with the optimization of process parameters for maximum productivity (given by the product of scanning velocity and cross feed) in laser transformation hardening. The process parameters considered are laser beam power, P; laser beam diameter, D_b; and the heat intensity distribution, namely, normal, bimodal, or uniform. A thermal analysis of the laser surface transformation hardening of gears was conducted (based on Jaeger’s classical moving heat source method) by considering the laser beam as a moving plane (disc) heat source to establish the temperature rise distribution in the workpiece (gear) of finite width. In a recent investigation [Int. J. Heat Mass Transfer 44 (2001) 2845], the authors considered the case of a heat source with a pseudo-Gaussian (or normal) distribution of heat intensity. The analytical results were compared with the experimental results published in the literature. In laser heat treatment of steel, it is generally considered preferable to use a wider heat intensity distribution, such as uniform or bimodal, for it enables more uniform case hardening depth. In this paper, this model is extended to cover bimodal and uniform distributions and compared with the normal distribution. Scanning velocities for no surface melting and for a case hardening depth of 0.1 mm were determined for surface transformation hardening of AISI 1036 (EN 8) steel for a range of laser beam powers, P, laser beam diameters, D_b, and various heat intensity distributions. Since diffusion during the heat treatment (surface transformation hardening) process is a time dependent phenomenon, based on the literature review, an interaction time of 15 ms was taken as a basis. It is hoped that laser industry with adequate facilities available can validate the thermal analysis and subsequent optimization presented in this paper.     

Effects of surface treatments of galvanized steels on projection welding procedure

A group of projection welding experiments and joints tension-shear tests are carried out for cold-rolled steel sheets, galvanized steel sheets (GSS) without treatment, GSS with phosphating and GSS with surface greasing, respectively. The experimental results are regressively analyzed on the computers, then the projection welded joint tension-shear strength curve and the perfect welding currents range of each material are obtained. The results show that surface treatments of galvanized steels have effects on their spot weldabilities. Among the four kinds of materials, GSS with surface greasing have the worst spot weldability, for they need higher welding current and have a narrow welding currem range.     

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 文章对Q345C钢板表面产生的裂纹进行了宏观和光学显微镜分析。结果显示：裂纹产生的原因是加热之后在轧制过程中形成的折叠，1号裂纹上出现的大型杂质有可能是压入的氧化铁皮。     

通过氢处理改善α＋β型钛合金的拉伸性能

提出了一种新的细化α+β型钛合金显微组织的氢处理工艺:在合金的氢化β转变点以下0—40K的温度范围对合金渗氢处理,空冷至室温,最后在948K真空除氢。Ti-6Al-4V和Ti-5Al-2.5Fe合金经此工艺处理后,组织显著细化,屈服强度,拉伸强度及延伸率分别提高8—15％,5—13％,7—14％。     

高速钢激光表面熔凝层的显微结构SCIEI

本文对W_(18)Cr_4V高速钢进行激光表面熔凝处理,采用光学显微镜和透射电镜分析表明,熔凝层组织为极细的树枝晶。部分枝晶中心保留有δ铁素体。枝晶内为孪晶马氏体和少量位错马氏体,孪晶马氏体上沿孪晶面M_(23)C_6碳化物呈薄片状共格析出。枝晶臂间为富W,V和Cr合金元素的奥氏体和M_6C碳化物。     

碳离子注入对Ti—6Al—4V合金疲劳寿命的改善

3×10~(17)Cion/cm~2在80keV的能量下注入到Ti-6Al-4V合金中。在应力控制的拉-零试验条件下,发现C~+注入试样的疲劳极限提高了28%。利用扫描电镜、透射电镜和二次离子质谱等研究了试样在注入前后和疲劳前后的表面层微观组织与结构以及注入元素沿表面层深的浓度分布。结果表明,注入层的微观组织中含有大量的辐照损伤并有许多细小的TiC相颗粒;注入与未注入试样的裂纹源在低应力疲劳中出现在亚表面区;注入元素在循环载荷作用下向基体中扩散。     

Pb-Free solders: Part 1. Wettability testing of Sn−Ag−Cu alloys with Bi additions

Maximum bubble pressure, dilatometric, and meniscographic methods were used in the investigations of the surface tension, density, wetting time, wetting force, contact angle, and interfacial tension of liquid alloys of Sn−Ag−Cu eutectic composition with various additions of Bi. Density and surface tension measurements were conducted in the temperature range 250–900 °C. Surface tensions at 250 °C measured under a protective atmosphere of Ar−H₂ were combined with data from meniscographic studies done under air or with a protective flux. The meniscographic data with a nonwetted teflon substrate provided data on interfacial tension (solder-flux), surface tension in air, and meniscographic data with a Cu substrate allowed determinations of wetting time, wetting force, and calculation of contact angle. The calculated wetting angles from meniscographic studies for binary Sn−Ag eutectic and two ternary Sn−Ag−Cu alloys were verified by separate measurements by the sessile drop method under a protective atmosphere with a Cu substrate. Additions of Bi to both ternary alloys improve the wettability and move the parameters somewhat closer to those of traditional Sn−Pb solders.     

Pb-Free solders: Part II. Application of ADAMIS database in modeling of Sn−Ag−Cu alloys with Bi additions

The ADAMIS database was used for calculation of the surface tension of the quaternary Sn−Ag−Cu−Bi liquid alloys by Butler's model. The resultant data were compared with those from the maximum bubble pressure measurements from Part I. The same thermodynamic database was next applied for the calculation of various phase equilibria. It was established that the Bi addition to the ternary Sn−Ag−Cu alloys (Sn-2.6Ag-0.46Cu and Sn-3.13Ag-0.74Cu in at.%; Sn-2.56Ag-0.26 Cu and Sn-2.86Ag-O.40Cu in mass%) causes lowering of the melting temperature and the surface tension to make the tested alloys closer to, traditional Sn−Pb solders. The simulation of the solidification by Scheil's model showed that the alloys with the higher Bi concentration are characterized by the lifting-off failure due to the segregation of Bi at the solder/substrate boundary. Thus, in modeling of new Pb-free solders, a compromise among various properties should be taken into consideration.     

钛合金表面双层辉光离子渗铝的研究

利用双层辉光渗金属技术，以铝为源极、TC4(Ti-6Al-4V)为阴极、氩气为工作气体，依靠辉光放电和不等电位空心阴极效应在TC4表面形成合金层。采用X射线衍射和辉光放电光谱分析了合金层的相组成及渗层内Al元素的分布．并对其进行硬度测试。结果表明：渗层由Ti3Al和α-Ti组成；铝的含量可达18％；渗层厚度可达13μm；其硬度比经渗铝处理后的有了较大程度的提高。     

萃取技术处理低品位铜矿的设计实践

介绍了溶剂萃取技术在铜冶金中的应用,依据半工业实验报告,设计并提供了处理低品位铜矿的萃取流程及工艺参数控制,并确定了其设备的大小。