An ion microprobe study of the microchemistry of Ni-base superalloy-Al2O3 metal-matrix composites

The chemical microstructure of Ni-base superalloy/Al₂O₃ metal-matrix composites (MMCs) has been studied by scanning ion microprobe microanalysis, using the secondary ion mass spectrometry (SIMS) technique. The MMCs were fabricated using the transient-liquid-phase bonding (TLP) process, with B-doped superalloy powder as an interlayer. Boron was found to diffuse rapidly throughout the matrix to form boride phases, mostly at the grain boundaries in the matrix. These borides contain excess Cr (also Mo, Si, W) in comparison with the Ni alloy-matrix, but are depleted in Ni (also in Al and Co). Carbides form at the grain boundaries as thin platelets and inside the grains as fine particles. Chemical reaction occurs between the sapphire fibre and the matrix; formation of NiAl₂O₄ spinel at the interface is suggested. This interface reaction layer is friable and parts of it peel off during consolidation to become inclusions in the matrix near the fibre/matrix interface.     

Optimizing microstructure in spray-formed and squeeze-cast metal-matrix composites

This paper discusses the methods of optimizing microstructure in the manufacture of spray-formed and squeeze-cast A- and Ti-based metal–matrix composites (MMCs) for a range of automotive and aerospace applications. Three specific MMC material/process/product combinations are considered: spray-formed/extruded Al alloy/SiC particulate-reinforced MMCs for aerospace structural components; squeeze-cast Al alloy/SiC particulate- and Al₂O₃ fibre-reinforced MMCs for automotive components; and spray-formed/diffusion-bonded Ti alloy/SiC fibre-reinforced MMCs for aeroengine components. Important features, which are emphasized in each case, are (i) using specific end applications to define desirable property and therefore microstructural goals; (ii) understanding the underlying process physics to control the resulting mechanisms of microstructural development; and (iii) using numerical modelling and associated experimental validation to allow subsequent implementation of process control systems.     

Scanning ion microprobe analysis of composite materials

Applications of scanning ion imaging with high lateral resolution in the microchemical investigation of metal – and ceramic-matrix composites are described. The technique, which combines a scanning ion microprobe with secondary ion mass spectrometry (SIMS), is ideally suited to the study of complex, multicomponent composite structures. Most elements can be detected with good sensitivity, enabling the determination of spatial distributions for major and minor elements. Analytical images obtained with this technique reveal unprecedented chemical information about interfacial segregation and interdiffusion phenomena. As examples, the characterization of both ceramic–matrix (Al borate–SiC) and metal–matrix (Ni alloy–Al₂O₃) composite materials is described.     

The microstructures of locally reinforced squeeze-cast Al-alloy metal-matrix composites

Locally reinforced metal-matrix composites (MMCs) have been manufactured by squeeze casting an A357 Al alloy into a die containing a reinforcement insert of either steel, an A356/10 vol.% SiC_p MMC, or a 20 vol.% Al₂O₃ short-fibre preform. The temperatures of the Al-alloy matrix, reinforcement insert and die were monitored continuously during squeeze casting, and the microstructures of the ascast MMCs were examined. Application of high pressure caused intimate contact along the insert-matrix interface with refinement of the matrix microstructure. There was little bonding between the matrix and the steel insert, while good bonding was obtained between the matrix and the A356/SiC_p MMC insert, which was partially melted at the interface. The Al₂O₃ short-fibre preform insert was fully infiltrated at high pressure, with a band of high Si content in the matrix microstructure near the interface.     

Characterization and microanalysis of interfacial reactions in metal–matrix composite systems

Understanding the solid-state reactions involved in metal/ceramic systems is important when combining the two types of materials into a composite. In this investigation, the solid-state reaction between Al₂O₃ (alumina) and a β-Ti alloy has been characterized by transmission electron microscopy (TEM), scanning electron microscopy, parallel-acquisition electron energy-loss spectroscopy and X-ray energy-dispersive spectroscopy. Two different systems were used to investigate this reaction. The first system utilizes a controlled reaction geometry and involved diffusion bonding single-crystal α-alumina and a β-Ti alloy. Here, three interfacial regions were found to form: a region of intermetallics (Ti₃Al and TiAl) located near the alumina interface, an α-Ti region, and a β-Ti region (rich in Mo, the β-phase stabilzer). Analysis of cross-section TEM samples of this reaction revealed the presence of both Ti₃Al and TiAl at the alumina interface. Orientation relationships between the intermetallics and the alumina are discussed. In the second, system, interfacial reactions inside metal–matrix composites that contain alumina and a β-Ti alloy were investigated. Here, different coatings used in the MMCs are investigated for their ability to prevent the reaction between the matrix and fibres. Reaction products inside the MMCs are compared with those found in the model reaction geometry.     

铜合金表面元素的飞行时间二次离子质谱微区原位分析

铜合金中含有Pb、Sn、Zn、Ni等元素,其分布和相对含量对铜合金的性能具有重要影响。本工作采用飞行时间二次离子质谱（TOF-SIMS）法对铜合金标准样品GBW02137和GBW02140的表面进行了微区原位分析;采用束斑直径约5 μm的一次离子束轰击500 μm×500 μm区域内的混合固体合金样品,实现了Cu、Pb、Ni、Sn和Zn元素的表面成像,并测量了各元素在铜合金样品表面的分布情况;利用标样校准法对GBW02137、GBW02140中的⁶⁴Zn/¹²⁰Sn、²⁰⁸Pb/¹²⁰Sn值进行相对含量分析。实验结果表明：TOF-SIMS法可用于铜合金中Cu、Pb、Ni、Sn和Zn等元素的表面成像和相对含量测定;采用标样校准法进行相对含量分析时,测得的⁶⁴Zn/¹²⁰Sn相对误差小于5.1%,RSD优于2.5%,²⁰⁸Pb/¹²⁰Sn的测量相对误差较大,接近27%,但其RSD仍低于5%。