Developments in Processing of Functionally Gradient Metals and Metal–Ceramic Composites:A Review

Functionally gradient/graded materials(FGMs), an emerging new class of materials, are the outcome of the recent innovative concepts in materials technology. FGMs are in their early stages of evolution and expected to have a strong impact on the design and development of new components and structures with better performance. FGMs exhibit gradual transitions in the microstructure and/or the composition in a specific direction, the presence of which leads to variation in the functional performance within a part. The presence of gradual transitions in material composition in FGMs can reduce or eliminate the deleterious stress concentrations and result in a wide gradation of physical and/or chemical properties within the material. Functionally graded metal–ceramic composites are also getting the attention of the researchers. Among the fabrication routes for FGMs such as chemical vapour deposition, physical vapour deposition, the sol–gel technique, plasma spraying, molten metal infiltration, self propagating high temperature synthesis, spray forming,centrifugal casting, etc., the ones based on solidification route are preferred for FGMs because of their economics and capability to make large size products. The present paper discusses and compares various solidification processing techniques available for the fabrication of functionally gradient metals and metal–ceramic composites and lists their properties and possible applications. The other processing methods are briefly described.     

Microstructure and shear strength of the brazed joint of Ti（C,N）-based cermet to steel

Firm joins were obtained between Ti(C,N)-based cermet and steel with Ag-Cu-Zn-Ni filler metal by vacuum brazing. The effects of technological parameters such as brazing temperature, holding time, and filler thickness on the shear strength of the joints were investigated. The microstructure of welded area and the reaction products of the filler metal were examined by scanning electron microscopy (SEM), metallographic microscope (OM), energy-dispersive X-ray analysis (EDS), and X-ray diffraction (XRD). The brazing temperature of 870°C, holding time of 15 min, and filler thickness of 0.4 mm are a set of optimum technological parameters, under which the maximum shear strength of the joints, 176.5 MPa, is achieved. The results of microstructure show that the wettability of the filler metal on Ti(C,N)-based cermet and steel is well. A mutual solution layer and a diffusion layer exist between the welding base materials and the filler metal.     

Finite Element Analysis of Push-Out Test of SiC Fiber Reinforced Titanium Matrix Composites

Based on the interphase layer model and the spring layer model, an improved interface model was developed to evaluate the interfacial shear strength of Titanium matrix composites(TMCs) and to analyze the effects of various parameters on the interfacial properties. The results showed that the improved interface model is more suitable for calculating the interfacial properties of SiC fiber reinforced titanium matrix composites. The interfacial shear strength of SiC/Timetal-834 predicted is 500 MPa. In additio...     

Finite Element Simulations of Crack Propagation in Al_2O_3/6061Al Composites

In this work, the local fracture initiation behaviour of an Al2O3/6061 Al composite is studied numerically. The damage behaviour of the microstructure is evaluated in consideration of the path and the amount of damage as well as the stress–strain performance of the microstructure. The damage behaviour of the ductile matrix has been simulated using the damage parameter D. For the simulation of fracture of the ceramic particles, a normal stress criterion is applied. For the analysis of the damage behaviour of the transition zone between particulate and matrix, both damage models(D parameter and normal stress criteria) are applied in this region. Parameter studies of crack propagation prediction in the Al2O3/6061 Al composite on the basis of an Element Elimination technique have been performed for two differently heat-treated variants resulting in different mechanical properties. In addition, residual stress effects on the damage behaviour are examined for various microstructural situations.     

Manufacture of Nano-Sized Particle-Reinforced Metal Matrix Composites:A Review

Compared to the micro-sized particle-reinforced metal matrix composites, the nano-sized particle-reinforced metal matrix composites possess superior strength, ductility, and wear resistance, and they also exhibit good elevated temperature properties. Therefore, the nano-sized particle-reinforced metal matrix composites are the new potential material which could be applied in many industry fields. At present, the nano-sized particle-reinforced metal matrix composites could be manufactured by many methods. Different kinds of metals, predominantly A1, Mg, and Cu, have been employed for the production of composites reinforced by nano-sized ceramic particles such as carbides, nitrides, and oxides. The main drawbacks of these synthesis methods are the agglomeration of the nano-sized particles and the poor interface between the particles and the metal matrix. This work is aimed at reviewing the ex situ and in situ manufacturing techniques. Moreover, the distinction between the two methods is discussed in some detail. It was agreed that the in situ manufacturing technique is a promising method to fabricate the nano-sized particle-reinforced metal matrix composites.     

Development of Flake Powder Metallurgy in Fabricating Metal Matrix Composites:A Review

Powder metallurgy(PM) is one of the most applied processes in the fabrication of metal matrix composites(MMCs). Recently, a novel PM strategy called flake PM was developed to fabricate MMCs with nano-laminated or hierarchical architectures. The name ‘‘flake PM' was derived from the use of flake metal powders, which could benefit the uniform dispersion of reinforcements in the metal matrices and thus result in balanced strength and ductility. Flake PM has been proved to be successful in the dispersion of nano aluminum oxides, carbon nanotubes, graphene nano-sheets, and microsized B4 C particles in aluminum or copper matrix. This paper reviews the technique and mechanism developments of flake PM in previous studies, and foresees the future develop of this new fabricating method.     

陶瓷基复合材料纤维拔出有限元研究

采用粘结带模型描述复合材料界面的分离特性，利用有限元数值方法模拟了陶瓷基复合材料的纤维拔出的细观损伤和破坏过程，计算了其拔出过程的载荷一位移响应曲线，研究了界面结合强度、纤维的埋深长度以及热膨胀不匹配对纤维拔出过程的影响。结果表明该模型能很好的解释纤维拔出的破坏过程，纤维的最大拔出力和材料的承载能力都随面结合强度、纤维的埋入长度和基体的热膨胀系数增大而增大；纤维与基体热膨胀系数的不匹配对摩擦拔出力有直接影响。     

一种新型液态金属浸渗网络结构预制体制备复合材料装置的设计

根据机械设计理论和液压知识,开发和设计了一种制备网络结构陶瓷增强金属基复合材料的新型装置。利用油缸液压和真空负压,成功实现了液态金属的浸渗。     

金属基复合材料的研究现状与发展

对金属基复合材料的分类、制造方法进行综述,阐述国内外研究现状,提出在重金属复合材料的研究中存在的问题,探讨对重金属基复合材料的研究方向.     

铸造法制备金属基复合材料的研究现状

综述铸造法制备金属基复合材料的各种工艺,如液态浸渗法、搅拌铸造法、离心铸造法、中间合金法、喷射分散法和铸渗法.指出其仍普遍存在的一些问题,并提出超声波在铸造法制备金属基复合材料中具有重要作用.随着研究的深入,这种超声复合法必将得到更广泛的应用.     

激光冲击SiCp/Cu复合材料的有限元模拟

为了探究激光冲击强化对SiCp/Cu复合材料力学性能的影响,采用有限元分析软件ANSYS/LS-DYNA对复合材料单胞模型进行冲击加载,模拟结果显示:在基体金属上存在着广泛的压应力,并且在载荷作用过程中导致了基体的屈服强化,大大提高了基体的强度;在基体与颗粒增强体之间的界面上存在着一定的等效应力值。采用WDW-200微机控制式电子万能试验机对激光冲击强化前后的试样进行拉伸性能对比试验:发现冲击后试样的抗拉强度较未冲击试样的提高了18MPa,且断口呈现韧窝形貌,为微孔聚集形韧性断裂。结果表明:激光冲击强化提高了SiCp/Cu复合材料的力学性能。     

自生金属基复合材料的研究进展

综述金属基自生复合材料的熔铸法制备工艺 ,国内、国外相关研究情况 ,应用的最新进展。在分析存在的问题的基础上 ;提出开展“可设计材料”研究的思路。