激光快速成型TC4钛合金的力学性能

金属零件的激光快速成型是结合CAD／CAM、高功率激光熔覆和快速原型制造的先进技术。研究了用激光快速成型技术制造TC4钛合金的力学性能，分析了低温退火和热等静压处理对力学性能的影响，并且测量了成型后试件的含氧量，观察了拉伸试件的断口形貌。研究结果表明激光快速成型制造的TC4钛合金的力学性能高于铸造组织的力学性能，达到了锻造组织的力学性能。     

Phase Evolution and Mechanical Properties of Nano-TiO2 Dispersed Zr-Based Alloys by Mechanical Alloying and Conventional Sintering

The present study deals with the synthesis of 1.0 to 2.0 wt pct nano-TiO₂ dispersed Zr-based alloy with nominal compositions 45.0Zr-30.0Fe-20.0Ni-5.0Mo (alloy A), 44.0Zr-30.0 Fe-20.0Ni-5.0Mo-1.0TiO₂ (alloy B), 44.0Zr-30.0Fe-20.0Ni-4.5Mo-1.5TiO₂ (alloy C), and 44.0Zr-30.0Fe-20.0Ni-4.0Mo-2.0TiO₂ (alloy D) by mechanical alloying and consolidation of the milled powders using 1 GPa uniaxial pressure for 5 minutes and conventional sintering at 1673 K (1400 °C). The microstructural and phase evolution during each stage of milling and the consolidated products were studied by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM), and energy-dispersive spectroscopy. The particle size of the milled powder was also analyzed at systemic intervals during milling, and it showed a rapid decrease in particle size in the initial hours of milling. XRD analysis showed a fine crystallite size of 10 to 20 nm after 20 hours of milling and was confirmed by TEM. The recrystallization behavior of the milled powder was studied by differential scanning calorimetry. The hardness of the sintered Zr-based alloys was recorded in the range of 5.1 to 7.0 GPa, which is much higher than that of similar alloys, developed via the melting casting route.     

无压浸渗法制备SiCp/Al复合材料的微观组织与力学性能

采用无压浸渗方法制备了SiC颗粒增强铝基复合材料，研究了材料的微观组织和力学性能。结果表明，复合材料浸渗完全，SiC颗粒分布均匀，无偏聚现象。铸造态复合材料中存在界面反应，经过透射电镜观察和XRD分析确认该界面反应物为MgAl2O4。界面反应的存在提高了润湿性，促进了无压自发浸渗。高温热暴露处理可以提高复合材料的布氏硬度，热暴露处理后的界面反应物呈块状弥散分布，但是反应物的数量略有增加。     

偏压参数对多弧离子镀CrN薄膜力学性能的影响

利用研发的多弧离子镀设备在高速钢基材上制备CrN薄膜,研究偏压参数对CrN薄膜表面形貌和力学性能的影响。结果表明,在偏压参数幅值增加的过程中,薄膜表面大颗粒的数量和尺寸呈现先减小后增大的变化趋势,薄膜硬度和结合力均呈现先增大后减小的变化趋势。残余应力随着偏压参数幅值的增加而逐渐增大。     

等离子喷涂纳米ZrO2热障涂层的组织及性能研究

采用大气等离子喷涂技术制备纳米ZrO2热障涂层,采用金相显微镜、X射线衍射仪、拉伸试验机等对涂层组织及性能进行了研究。结果表明,纳米ZrO2热障涂层组织均匀,面层内孔隙较小、呈近圆形,孔隙率为9.6%;涂层由t-ZrO2单相组成,其平均结合强度和平均剪切强度较传统微米ZrO2热障涂层分别提高63.5%和50.5%,分别达到46.63MPa和23.97MPa;同时涂层具有优异的抗腐蚀性能和耐湿热能力,腐蚀和湿热试验后涂层完整、表面清洁,无新相生成。     

Mechanical Properties and Microstructural Characterization of Cu-4.3 Pct Sn Fabricated by Selective Laser Melting

Components were fabricated via selective laser melting (SLM) of prealloyed Cu-4.3 pct Sn powder and heat treated at 873 K and 1173 K (600 °C and 900 °C) for 1 hour. Tensile testing, conductivity measurement, and detailed microstructural characterization were carried out on samples in the as-printed and heat-treated conditions. Optimization of build parameters resulted in samples with around 97 pct density with a yield strength of 274 MPa, an electrical conductivity of 24.1 pct IACS, and an elongation of 5.6 pct. Heat treatment resulted in lower yield strength with significant increases in ductility due to recrystallization and a decrease in dislocation density. Tensile sample geometry and surface finish also showed a significant effect on measured yield strength but a negligible change in measured ductility. Microstructural characterization indicated that grains primarily grow epitaxially with a submicron cellular solidification substructure. Nanometer scale tin dioxide particles identified via X-ray diffraction were found throughout the structure in the tin-rich intercellular regions.

     

Microstructure and Mechanical Properties of Aluminum/Copper Composite Rod Fabricated by Axisymmetric Spiral Extrusion

In the present investigation, an axisymmetric spiral extrusion was used for fabrication of bimetallic Al/Cu composite rods. In this process, a cylindrical bimetallic sample was extruded through an extrusion die having engraved spiral grooves to produce near net shaped composite part. After preparation of composite rods, the bonding strength was evaluated by applying shear stress on Al/Cu interface using compression test. Also the bonding interface was examined by optical metallography and scanning electron microscopy. The results showed that the bond strength increased in Al/Cu composite rods after spiral extrusion and the bonded interface was free of intermetallic layer. The stress imposed on interface region during spiral extrusion broke the work hardened layer in the mating surfaces, and consequently, the cold weld was established between virgin Al and Cu in the contact area. The obtained results showed a feasibility of spiral extrusion processing for production of Al/Cu bimetallic composite rods.     

机械合金化法制备Ag/SnO_2(12)材料的组织与性能研究

采用机械合金化、冷等静压成型、烧结、热挤压等粉末冶金技术集成的方法制备Ag/SnO2(12)材料,并对其组织与性能进行研究。研究结果表明:通过机械合金化的方法获得的Ag/SnO2(12)复合粉末,粉末颗粒形状不规则,为多层片状银的叠加,粒径的范围在20～50μm,SnO2颗粒细小且均匀弥散镶嵌于Ag基体中;Ag/SnO2(12)复合材料中SnO2颗粒细小,组织均匀,力学性能良好,但由于材料采用粉末冶金方法制备,不可避免的存在少量的孔隙,从而影响了材料的电学性能,电阻率偏高;其断口形貌为解理脆性断裂(宏观)和准解理断裂(微观)的综合。     

Microstructure and Mechanical Properties of CNTs/A356 Nanocomposites Fabricated by High-Intensity Ultrasonic Processing

Carbon nanotube (CNT)-reinforced A356 alloy nanocomposites were successfully fabricated by introducing a method of CNT predispersion and high-intensity ultrasonic treatment. The scanning electron microscope and energy-dispersive spectrometer results showed that high-intensity ultrasonic treatment was able to disperse the CNTs into the melt. When the ultrasonic power was less than 2.1 kW, the microhardness and tensile properties (ultimate tensile strength (UTS), yield strength (YS), and elongation) of the nanocomposites improved as the ultrasonic power increased. Further, the microhardness, UTS, and YS improved as the CNT content increased while elongation decreased. The microhardness, UTS, and YS of the 0.8 wt pct CNTs/A356 nanocomposites fabricated by high-intensity ultrasonic processing at an ultrasonic power of 2.1 kW were increased, respectively, by 27.8, 17, and 29.2 pct compared to the A356 alloy without CNT addition, and the ductility remained. The fracture analysis confirmed that CNTs were homogeneously distributed in the matrix, and strong interfacial bonding formed between CNTs and the matrix. Also, transmission electron microscope results confirmed that CNTs were stale embedded in the matrix and the formation of brittle Al₄C₃ was suppressed.

     

Microstructural and Mechanical Properties of Ni-Base Thermal Spray Coatings Deposited by Flame Spraying

In this work, two different Ni-base powders, namely, ProXon 21021 (P21) and ProXon 21031 (P31), were sprayed onto a steel substrate 35CrMo4 using a thermal flame spray technique. The morphology and chemical composition of the phases that are present in the powders and coatings were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The hardness and wear resistance of the coatings were investigated. The XRD analysis revealed that the phases present in the coatings are different from the initial powders. In addition, some inhomogeneities such as oxides, porosity, and unmelted particles were observed by SEM. It was found that the P31 spray-coated exhibited higher microhardness, higher wear resistance, and significantly lower friction coefficient in comparison with those of P21 coatings.     

Effect of Thin Polymer Coatings on the Mechanical Properties of Steel Plates

The influence of powder coatings based on an epoxide polyester mixture on the mechanical properties of the plates made of rolled sheet steel is studied. The influence of 100-μm-thick coatings on the mechanical properties of specimens 0.7–1.5 mm thick is considered. The bending and tensile tests performed at room and elevated temperatures show that the thin coatings weakly affect the mechanical properties of the plates. In particular, the stiffness of the coated plates during tension and bending remains almost the same despite the fact that the elastic modulus of the coated plates is always slightly lower than Young’s modulus of steel because of an increased specimen thickness determined with allowance for the presence of a coating. The influence of the coatings is substantial in compressive stability tests. Under supercritical deformation conditions, the bearing capacity of the coated plates decreases substantially, and their critical stability load on the loss of stability falls by 20–30% (depending on the substrate thickness). This effect can be explained by the influence of the residual thermal stresses that appear in the specimens during coating deposition.     

Pressureless Infiltration and Resulting Mechanical Properties of Al-AlN Preforms Fabricated by Selective Laser Sintering and Partial Nitridation

A novel manufacturing process has recently been developed for the fabrication of intricate Al-AlN composite parts. The process involves green shape formation by selective laser sintering, preform development by nitridation, and net shape forming by pressureless infiltration. The infiltration atmosphere has an important influence on the final fabrication and mechanical properties. This work presents a detailed investigation on the infiltration of Al-AlN preforms with AA 6061 at various temperatures above its liquidus under nitrogen, vacuum, and argon. The green shapes are formed by selective laser sintering of a premix of AA 6061-2Mg-1Sn-3Nylon (wt pct) powders. They are then partially nitrided to create a rigid, 2- to 3-μm-thick AlN skeleton for subsequent infiltration. Nitrogen infiltration results in the highest density (2.4 gcm⁻³) and best tensile properties (UTS: 214 MPa; elongation: 2.5 pct), while argon infiltration gives the lowest density. Fractographs confirmed the difference in density arising from the use of different atmospheres where small pores are evident on the fracture surfaces of both argon and vacuum-infiltrated samples. The molten AA 6061 infiltrant reacts with nitrogen during infiltration leading to a 5-μm-thick AlN skeleton compared to the original 2- to 3-μm-thick skeleton in both argon and vacuum-infiltrated samples. Transmission electron microscope (TEM) examination revealed inclusions of Mg₂Si and Mg₂Si _x Sn_1−x in both nitrogen- and argon-infiltrated samples but not in vacuum-infiltrated samples. Vacuum infiltration is slower than nitrogen and argon infiltration. The mechanisms that affect each infiltration process are discussed. Infiltration under nitrogen is preferred.     

Microstructure and Mechanical Properties of Yttria-Stabilized Zirconia Coatings Produced by Eletrophoretic Deposition and Microwave Sintering

Y₂O₃-stabilized zirconia coatings were deposited on superalloy K17 substrates at room temperature by the eletrophoretic deposition technique followed by two different sintering methods. Scanning electron microscopy, X-ray diffraction (XRD), and nanoindentation techniques were employed to characterize morphological, structural, and mechanical properties of the coatings. Finer and more uniform microstructures were observed in the microwave sintered coatings. For the conventionally sintered coatings, the monoclinic phase was observed. The microwave sintered coatings of Y₂O₃-stabilized zirconia contain mainly cubic/tetragonal phases with some metastable phase present. In comparison with the hardness of 3.1 GPa and elastic modulus of 83.5 GPa for conventional sintered coating, the hardness and elastic modulus for microwave sintered coating rapidly increased to 4.3 and 172.7 GPa, respectively. Such coatings have potential in being used as thermal barrier coatings (TBCs) on superalloy substrates.     

Magnetic Properties of Highly Dispersed Ferromagnetics Obtained by the Thermochemical Method

The magnetic properties of highly dispersed powders of iron and iron compositions with silver, platinum, gold, copper, and zinc, obtained by the thermochemical method, are studied. Highly dispersed ferromagnetics are in the class of hard magnetic materials with a particle size of 0.02-0.20 µm. Hence, they fall into the category of single-domain or quasi-single-domain formations. These powders, which have now been produced for the first time, can be used in surgery, endocrinology, oncology, and other fields.     

Mechanical Properties and Wear Resistance of Microarc Diffusion Coatings on Steel

Metallurgist - The aim of the work is to study the influence of the structure and phase composition of diffusion coatings prepared by microarc surface alloying of steel with carbon, boron and...     

Microstructure,Mechanical Properties,and Sliding Wear Behavior of Oxide-Dispersion-Strengthened FeMnNi Alloy Fabricated by Spark Plasma Sintering

Metallurgical and Materials Transactions A - The face-centered-cubic (fcc) CoCrFeMnNi high-entropy alloy suffers from low strength and wear resistance at ambient temperature. Herein, we developed a...