多组分铜基金属粉末选区激光烧结致密化机理

研究了选区激光烧结专用多组分铜基金属粉末(组分包括纯Cu,预合金CuSn,CuP)的烧结性能.结果表明,通过合理控制激光工艺参数(特别是激光功率和扫描速率),能顺利实现粉末烧结成形,且无明显的"球化"效应和翘曲变形.扫描电镜和X射线衍射分析证实,此组粉末体系的激光烧结是基于液相烧结机制,其中熔点较低的CuSn充当粘结金属,熔点较高的Cu充当结构金属;而添加元素P则起稀释剂的作用,能避免Cu颗粒表面氧化.研究了粉末体系中粘结金属含量对粉末烧结致密化和烧结件微观组织的影响.结果表明,在一定范围内粘结金属含量的提高有利于改善烧结致密度;但若粘结金属过量,则会因"球化"效应而降低致密度.     

烧结温度对Micro-FAST制备钛微型齿轮致密化的影响

将新颖的多物理场活化烧结微成形技术(Micro-FAST)引入到钛微型齿轮的制备中,研究了烧结温度对Micro-FAST制备钛微型齿轮致密化的影响。结果表明,在1200℃烧结保温4 min,体系的相对密度即可达到90.5%。Micro-FAST的烧结致密化过程大致可分为4个阶段:预热阶段、低温保温阶段、快速升温阶段和烧结保温阶段,钛粉末的致密化过程主要发生在快速升温阶段。对烧结体系的收缩动力学曲线研究发现,在电场、力场和温度场的耦合作用下,粉末体系在450℃发生了塑性变形,在1032℃生成了局部液相。研究表明,与传统烧结法相比,多物理场活化烧结法是一种新型和高效的制备钛微型零件的良好方法。     

超音速火焰喷涂316L不锈钢涂层性能研究

采用超音速火焰喷涂技术(HVOF)在高强钢表面制备了316L不锈钢涂层,利用扫描电镜、显微硬度仪、电化学测试系统等设备对涂层金相组织、硬度、结合性能和抗腐蚀性能等进行了测试,并分析了WC-CoCr中间层对316L不锈钢粉末涂层结合强度及涂层界面的影响。结果表明:超音速火焰喷涂316L不锈钢粉末颗粒在喷涂中变形充分,形成较致密的涂层,并具有超过400 HV0.1的显微硬度;涂层具有较高自腐蚀电位,耐蚀性优于高强钢;涂层结合强度随着涂层厚度的减小、基体硬度的增加而提高;WC-CoCr底层可改善涂层界面结合,从而改善316L不锈钢涂层的结合性能。     

Al、Cu二元合金系烧结过程的原位观察

利用高温光学显微镜(HTOM)对由纯铝粉和纯铜粉制得的二元粉末体系进行了原位烧结试验,原位观察结果表明:经典烧结理论对塑性粉末体系不再适用;该体系烧结的典型物理过程可概括为颗粒边界熔化、晶界熔化、颗粒熔化,最后为合金元素铜的扩散均匀化,而这四个阶段在时间上并不能严格分开,而是交叠进行的;边界熔化受颗粒表面氧化膜破碎、表面曲率和颗粒变形等因素影响;晶界扩散在烧结过程中始终起着非常重要的作用。这些结果为进一步合理制定和优化烧结工艺提供了直接的参照依据。     

纳米晶Mo-Cu复合粉末烧结行为的研究

采用溶胶-喷雾干燥-煅烧-氢气还原的方法制备了纳米晶Mo-18Cu、Mo-30Cu、Mo-40Cu复合粉末,研究了纳米晶Mo-Cu粉末的烧结行为以及Cu含量对致密化的影响.结果表明,纳米晶Mo-Cu复合粉末致密化程度高,速度快,在1050～1200 ℃烧结,Mo-30Cu和Mo-40Cu的相对密度可达98%以上,且合金晶粒细小,而Mo-18Cu在1350 ℃以上烧结,相对密度也可达98%以上,但晶粒聚集长大到5 μm左右.研究发现Mo-Cu复合粉末形成了亚稳态的超饱和Mo(Cu)固溶体,随着烧结温度的升高,Cu相逐渐从亚稳态的超饱和Mo(Cu)固溶体颗粒中析出.     

Al、Cu二元合金系烧结过程的原位观察

利用高温光学显微镜（HTOM）对由纯铝粉和纯铜粉制得的二元粉末体系进行了原位烧结试验,原位观察结果表明：经典烧结理论对塑性粉末体系不再适用;该体系烧结的典型物理过程可概括为颗粒边界熔化、晶界熔化、颗粒熔化,最后为合金元素铜的扩散均匀化,而这四个阶段在时间上并不能严格分开,而是交叠进行的;边界熔化受颗粒表面氧化膜破碎、表面曲率和颗粒变形等因素影响;晶界扩散在烧结过程中始终起着非常重要的作用.这些结果为进一步合理制定和优化烧结工艺提供了直接的参照依据.     

喷雾造粒粉末对粉末冶金316L不锈钢组织及力学性能的影响

研究了造粒粉末对粉末冶金316L不锈钢密度、硬度和微观组织的影响。在316L粉末中添加质量分数分别为0%、20%、40%、60%、80%、100%的造粒粉末,经压制后在1205℃进行烧结。结果表明:添加造粒粉末降低了316L不锈钢的生坯密度,但样品仍有很好的成形性与保形性。随造粒粉末含量的增大,样品的密度和硬度也随之提高。当添加100%造粒粉末时,316L不锈钢的密度和硬度最高,分别为7.607 g/cm~3、71 HRB。     

Ti6Al4V钛合金粉末烧结体镦粗过程致密化规律研究

利用Deform-3D软件对Ti6Al4V粉末烧结体镦粗变形过程进行了热力耦合模拟,分析了不同变形参数下粉末烧结体镦粗变形的致密化行为及规律。结果表明:粉末烧结体在镦粗过程中,各区域密度、应力、应变分布不均匀;致密过程中密度分布与应变分布一一对应,且密度应变与体积应变成线性关系;致密过程受变形程度、变形温度、初始相对密度及变形速度等因素的影响。     

烧结工艺对316L不锈钢3DP打印件性能的影响

基于3DP技术制备出316L不锈钢生坯,并将其固化、脱脂,然后在1 385、1 410、1 435℃下进行高真空烧结,探索打印生坯采用无压烧结致密化的可行性,探究烧结工艺对试样密度、力学性能和拉伸断口的影响。结果表明,打印毛坯通过无压烧结来实现致密化是可行的。随着烧结温度增加,试样的致密度提高、尺寸收缩增大,材料的强度、塑性等力学性能也随之大幅改善,在1 435℃烧结时其致密度最大,达到88.7%,体积收缩率为37.0%,屈服强度为160 MPa,接近商用316L不锈钢(177 MPa)的水平,抗拉强度为355 MPa,伸长率达到26.4%。     

镁对氢化钛烧结致密化的影响

以氢化钛粉末和镁粉为原料,利用模压工艺制备纯钛,主要研究了镁对氢化钛粉末烧结致密化的影响。结果表明,少量镁的添加能够促进氢化钛粉末的烧结致密化,而过量镁则降低烧结密度,镁添加量为0.5%(质量分数,下同)时效果最优,将烧结体相对密度由96.5%提高到98.7%。通过对烧结过程动力学、镁还原氧化钛反应的热力学和动力学,以及烧结体成分进行分析,发现少量镁促进氢化钛烧结致密化的机理为:真空烧结时镁从坯体中挥发,形成的镁蒸气对粉末颗粒表面的氧起到净化作用,提高了烧结活性,从而提高烧结密度。     

316L不锈钢25～350℃中的拉伸行为及流变应力计算

通过高温试验装置在模拟井下工况温度25～350℃范围内进行了316L不锈钢的拉伸试验。结合拉伸试验数据、拉伸后微观结构以及断口形貌对316L不锈钢的25～350℃范围内的拉伸变形行为进行了探讨。应用温加工变形理论,建立了316L不锈钢在井下温度场环境中的形变本构方程。基于拉伸试验数据,计算了应变速率因子Z,变形激活能Q,建立了316L不锈钢温变形过程的流变应力计算模型,为完井设计中膨胀管膨胀施工提供了参考依据。     

Nucleation of corrosion pits in Ringer’s solution containing bovine serum

The effects of the presence of bovine serum on the nucleation of corrosion pits on 316L stainless steel and commercially pure titanium in Ringer’s physiological solution at 37 °C are presented. The experiments involved measurement of current transients generated on microelectrodes under potentiostatic control below the pitting potential. Results show that the presence of the organic components of the serum stimulates the nucleation of pits on 316L stainless steel. A similar but smaller effect is shown for commercially pure titanium.     

不锈钢表面Cr-Pd合金电沉积及镀层在强还原性介质中的耐蚀性

通过选择络合剂、缓冲剂及采用方波脉冲电流和优化电镀工艺, 在酸性镀液中实现了Cr-Pd共镀, 并在不锈钢表面制备出均匀致密且与基体结合良好的Cr-Pd合金镀层. 通过改变镀液中铬盐和钯盐的相对含量, 可以大范围改变镀层成分. Cr-Pd合金镀层可显著提高不锈钢在高温还原性腐蚀介质中的耐蚀性, 在沸腾的20%(质量分数)H₂SO₄溶液中, Cr-Pd合金镀层使316L不锈钢的腐蚀速率降低了4个数量级以上. 镀层中的Cr和Pd对致钝具有协同促进作用, 当镀层中含有2.5%Pd(质量分数)时即具有明显的促进钝化效果, 含33.3%Pd镀层对不锈钢的保护效果与纯Pd镀层相当.     

大气等离子喷涂TiB2-316L不锈钢基复合涂层及其耐磨性能

分别采用高能球磨制备了TiB2含量(质量分数)为10%的316L不锈钢基复合粉,高能球磨与喷雾干燥造粒工艺制备了TiB2含量(质量分数)为40%的316L不锈钢基复合粉,大气等离子喷涂制备相应的TiB2-316L不锈钢基金属陶瓷涂层与316L不锈钢涂层.室温下采用高速环块磨损试验研究TiB2-316L不锈钢基金属陶瓷涂层的磨损特性.采用X射线衍射分析涂层物相,扫描电镜分析喷涂粉末、涂层结构和摩擦副磨损表面形貌.结果表明,大气等离子喷涂两种制粉工艺获得的316L不锈钢基TiB2复合粉能获得较耐磨的316L不锈钢基TiB2复合涂层,耐磨性高于316L不锈钢涂层,且TiB2在复合涂层中增强涂层耐磨性的原因是TiB2颗粒在涂层316L韧性基体中充当强化相,且TiB2在摩擦接触处摩擦氧化形成的氧化产物具有自润滑特性,能减少涂层的磨损量.     

Microstructure and Mechanical Properties of B-Bearing Austenitic Stainless Steel Fabricated by Laser Metal Deposition In-Situ Alloying

In the field repair application of laser metal deposition (LMD), the kinds of powder materials that can be used are limited, while the equipment components are made of various materials. Hence many components have to be repaired with heterogeneous materials. However, it is difficult to match the mechanical properties between the repaired layer and the substrate due to the different materials. Based on the high flexibility of raw materials and processes in LMD, an in-situ alloying method is proposed herein for tailoring the mechanical properties of LMDed alloy. Using different mixing ratios of Fe314 and 316L stainless steel powders as the control parameter, the microstructure and mechanical properties of B-bearing austenitic stainless steel fabricated by LMD in-situ alloying with different proportions of Fe314 and 316L particles were studied. With the increase in the concentration of 316L steel, the volume fraction of the eutectic phase in deposited B-bearing austenitic stainless steel reduced, the size of the austenite dendrite increased, the yield strength and ultimate tensile strength decreased monotonically, while the elongation increased monotonically. Moreover, the fracture mode changed from quasi-cleavage fracture to ductile fracture. By adding 316L powder, the yield strength, tensile strength, and elongation of deposited B-bearing austenitic stainless steel could be adjusted within the range of 712 MPa-257 MPa, 1325 MPa-509 MPa, and 8.7%-59.3%, respectively. Therefore, this work provides a new method and idea for solving the performance matching problem of equipment components in the field repair.     

不锈钢/碳钢TIG焊熔池表面流动行为

为研究异种钢在钨极惰性气体保护焊过程中的熔池表面流动行为,以粒子示踪法为基础,通过激光熔池表面反射的方法,对304不锈钢/Q235碳钢、316L不锈钢/Q235碳钢焊接过程中熔池表面液态金属的流动行为进行了研究,分析了熔池表面示踪粒子的运动趋势,并以此为依据计算了熔池表面液态金属的流动速度.结果表明,在不锈钢/碳钢的TIG焊过程中,熔池表面的液态金属存在从不锈钢侧流向碳钢侧的流动行为.其中,示踪粒子在304不锈钢/Q235碳钢的焊接熔池表面平均流动速度约为25.3 mm/s,在316L不锈钢/Q235碳钢的焊接熔池表面平均流动速度约为21.6 mm/s.     

粉末形貌对选区激光熔化316L不锈钢力学性能的影响

以气雾化316L不锈钢粉为原料,结合等离子球化和选区激光熔化技术制备了不锈钢块体,并用XRD、SEM、激光粒度仪、振实密度仪和万能力学试验机等对等离子球化粉体和选区激光不锈钢块的组织结构和性能进行了表征.结果表明:316L不锈钢粉经等离子球化处理后,不规则扁平状颗粒数量减少,球形颗粒数量增加,振实密度与松装密度的比值(...     

Production of Annealed Cold-Sprayed 316L Stainless Steel Coatings for Biomedical Applications and Their in-vitro Corrosion Response

316L powders were successfully deposited onto Al5052 aluminium substrates by cold spray method. Annealing was treated on the coated samples at 250–1000°C temperatures under Ar atmosphere. The in vitro performances of the coatings have been compared with using electrochemical corrosion test technique in the simulated body fluid (SBF) at body temperature (37°C). A scanning electron microscope (SEM-EDS) and X-ray diffraction (XRD) have been used for microstructural characterization and phases identifications of the coatings, respectively. The results were shown that there are high adhesions at particle and substrate interfaces and between the particles deposited as well. Also, the increasing annealing temperature increases corrosion resistance of the cold sprayed 316L stainless steel coatings. The corrosion susceptibility of the coating annealed at 1000°C was similar that of standard 316L stainless steel implant material in Ringer’s solution. The microstructural observations revealed that corrosion starts between the inter-splat powders and continues throughout the surface not in-depth.     

Effectiveness of electrically assisted solid-state pressure joining using an additive manufactured porous interlayer

A solid-state pressure joining using resistance heating as a heat source and adopting an additive manufactured metal porous interlayer between joining specimens is demonstrated. During the joining of 316L stainless steel cylindrical specimens, an electric current is directly applied to the joint under continuous axial compression. Defect-free joints are successfully fabricated with a lower joining pressure when applying the porous interlayer with a lower compressive strength and higher electric resistivity. The microstructural analysis confirms that the porosity is eliminated as a result of the compressive deformation during joining, and recrystallization takes place in the interlayer.     

Observation of corrosion behavior of stainless steels in a salt manufacturing plant environment using the multichannel electrode method

Crevice corrosion of four kinds of stainless steel, SUS316L, NAS64, NAS185N and NAS254N, in saturated NaCl solution at temperatures up to 100 °C was investigated using the multichannel electrode method. In this method, a pile of five individual working electrodes (WEs) of stainless steel sheet were embedded in epoxy resin and a small hole penetrating through the five WEs was treated as an artificial crevice. Time transition and distribution of the coupling current between the five WEs were measured as a function of crevice depth, kind of stainless steel, temperature and concentration of dissolved oxygen (DO). Anodic or cathodic coupling current on the five WEs of SUS316L changed depending on their corroding state. On the other hand, NAS64, NAS185N and NAS254N showed that the WE outside the crevice contributed as a cathode and that WEs inside the crevice contributed as an anode. The coupling current on SUS316L was strongly affected by concentration of DO, while the coupling current on NAS64, NAS185N and NAS254N was not affected by DO, probably due to the establishment of a passive state inside the crevice.