Ti14合金在等温热暴露条件下Ti2Cu相的粗化行为

研究了Ti14合金中Ti_2Cu相在500℃等温热暴露下的静态粗化行为,揭示出Ti_2Cu相的生长速率和形态变化受扩散机制控制。结果表明:静态粗化过程由快速粗化阶段和稳定粗化阶段组成,其中快速粗化阶段主要由末端迁移机制控制,由于条状Ti_2Cu相的末端与长轴方向界面能的差异,溶质原子的扩散过程导致板条状Ti_2Cu的粗化和破碎。而稳定粗化阶段主要由Oswald熟化机制控制,随着时间的延长,合金中Ti_2Cu析出物的尺寸持续增大,而粗化速率降低。Ti_2Cu相的快速粗化会引发第二相的强化,并有效提高快速粗化阶段的可塑性。但是在稳定粗化阶段,由于Ti_2Cu相的长大会增加其位错的有效滑移长度,并进一步影响其裂纹形核阻力同时改变界面构型和晶格失配,从而降低Ti14合金的拉伸塑性。     

Ti-6Al-7Nb合金高温塑性变形行为及热加工图研究

本文以Ti-6Al-7Nb合金为研究对象,采用Gleeble-3500热模拟压缩试验机进行不同温度和应变速率压缩试验。分析了Ti-6Al-7Nb合金在变形温度1023 K、1073 K、1123 K、1173 K,应变速率为0.005 s-1、0.05 s-1、0.5 s-1、5 s-1和10 s-1,最大变形量为60%下的高温变形行为及热加工特性。结果表明：变形温度与应变速率对Ti-6Al-7Nb合金的流动应力影响较大,其中应变速率是影响加工硬化过程的主要因素。Ti-6Al-7Nb合金在发生热塑性变形时后的物相主要有：初生α相、片层状α相、次生α相、片层状β相以及发生球化的初生α相等。Arrhenius本构方程模型适用于低温低应变速率和高温高应变速率形变条件的Ti-6Al-7Nb合金高温变形。利用MATLAB构建计算确定了合金最佳塑性变形区间为：应变速率0.0067 s-1-0.1353 s-1和温度1100-1173 K,在该区间有可能获取Ti-6Al-7Nb合金最佳的塑性变形工艺参数。     

Effect of laser remelting on the microstructure and corrosion resistance of plasma sprayed Fe-based coating

Fe-based amorphous and nanocrystalline coatings were fabricated by air plasma spraying. The coatings were further treated by laser remelting process to improve their microstructure and properties. The corrosion resistance of the as-sprayed and laser-remelted coatings in 3.5wt% NaCl and 1 mol/L HCl solutions was evaluated by electrochemical polarization analysis. It was found that laser-remelted coating appeared much denser than the as-sprayed coating. However, laser-remelted coating contains much more nanocrystalline grains than the as-sprayed coatings, resulting from the lower cooling rate in laser remelting process compared with plasma spraying process. Electrochemical polarization results indicated that the laser-remelted coating has great corrosion resistance than the as-sprayed coating because of its dense structure.     

Surface Strengthening of Ti-6Al-4V Alloy by Glow Plasma Carbonization Process

利用辉光等离子渗碳技术对Ti-6Al-4V进行了表面强化处理。等离子气体为氩气,渗碳温度和时间分别为950 ℃和3 h,工作压力为30~35 Pa。为了避免传统气体渗碳过程中易于产生氢脆的现象,用固体石墨棒作为碳源。渗碳结束后,分别利用OM、FESEM和XRD对渗碳层做分析,并在坏-块摩擦磨损试验机上对处理和未处理样品进行摩擦磨损对比实验。结果发现,渗碳层深度约为416 μm,其表面碳化物(TiC和V8C7)提高了合金表面的硬度和耐磨性能。     

基于层次分析法的混凝土拖泵性能评价

以国内外企业和3个国内企业的混凝土拖泵产品为例,利用层次分析法建立评价模型,对各企业产品进行性能评价,得到了各企业产品技术的满足度指数,并找出国内外混凝土拖泵技术水平的主要差距,为其产品性能提升提供一定的依据。     

钛合金阳极氧化的研究进展

钛合金具有密度低、比强度高等优点。钛合金的阳极氧化膜具有比钛基体更高的硬度、耐蚀性及耐磨性,而且可呈现各种颜色,是理想的保护层和装饰层,因而受到各行业的广泛关注。综述了钛合金阳极氧化技术的研究现状,介绍了阳极氧化的工艺流程。分别从电解电压、氧化时间、氧化温度、电流密度、电解液种类和电解液浓度等方面分析了影响阳极氧化膜层和颜色的因素。从膜层厚度、基体表面粗糙度和电解液化学成分等方面讨论了钛合金阳极氧化工艺的发展趋势。     

等离子喷涂对涂层非晶含量的影响

选用一种Fe基非晶粉末,利用等离子喷涂技术在不同喷涂电流和气体流量参数下制备涂层.用X射线衍射仪分析涂层非晶相对含量,对纯非晶涂层和含有纳米晶粒非晶复合涂层分别进行透射电镜观察.通过调整等离子喷涂电流和气体流量获得不同非晶含量非晶涂层,并分析其形成原因.     

放电等离子烧结42CrMo钢/黄铜双金属复合接头的显微组织

采用放电等离子烧结技术对42CrMo钢和黄铜进行连接,研究了接头的显微组织、成分和硬度分布,分析了其接头组织形成过程。结果表明:在42CrMo钢和黄铜之间存在一个宽10~20μm的过渡层,过渡层组织均匀细密;在近过渡层的黄铜中存在一个宽约70μm的岛状组织区,这些岛状组织主要为铁的固溶体;在较高压力下,接头中不存在缝隙,但存在少数孔隙;接头的截面硬度呈梯度变化;铁元素扩散深度达到90μm,铜元素扩散不太明显,42CrMo钢和黄铜之间为扩散连接。     

TC4钛合金电子束焊与TIG焊焊接接头的组织性能对比研究

针对TC4钛合金电子束焊及TIG焊焊接接头的凝固组织、微观相结构及接头静载室温拉伸性能进行了对比研究。结果发现,TIG焊接头热影响区内为较粗大的等轴晶,焊缝区内凝固组织为粗大柱状晶,柱状晶粒生长方向由最初的垂直于焊缝-热影响区界面逐渐转为垂直向上生长。电子束焊接头组织形态同样是热影响区为等轴晶粒形态,而焊缝区内为柱状晶粒,等轴晶和柱状晶粒的尺寸较TIG焊均明显减小,且柱状晶生长方向始终垂直于焊缝-热影响区界面。TIG焊焊缝区原始β晶内的微观组织由魏氏α板条、针状马氏体α’以及β基体组成,而电子束焊焊缝原始β晶内的微观组织由大量细长针状马氏体α’+β基体组成。力学性能测试结果表明,电子束焊焊接接头的强度略高于TIG焊,塑性显著优于TIG焊。     

Effects of heat-treatment on crystallization and wear property of plasma sprayed Fe-based amorphous coatings

The Fe-based amorphous coatings were produced by air plasma spraying. The as-sprayed coatings were heat-treated at the temperature of 573, 873, and 1 023 K, respectively. The crystallization and wear behavior of the heat-treated amorphous coatings were investigated. It was found that the amorphous-nanocrystalline transformation appeared when the as-sprayed coatings were treated at 853 K. The crystallization process had completed and a coating with microcrystallines was formed when the treatment temperature reached 1 023 K. The resultant amorphous and nanocrystalline composite coatings exhibited superior wear resistance compared to crystalline coating. It is attributed to fine grain strengthening of formed nanocrystallines.