Band 60, Heft 7

Production and structural investigations of Cu-based FeCr reinforced composite were performed by using mechanical alloying, optical microscope, scanning electron microscope, X-ray diffraction and hardness test. The increment in FeCr addition caused the increment in the cold deformation rate. This situation resulted in breakage of the powder particles throughout mechanical alloying. Thus, the grain dimension of the FeCr powders decreased and the Fe wt.% in the CuCr powders advanced. The collision force between the Cu-Cr powder and the grinding ball weakened with the increase of FeCr concentration and resulted as higher reinforcement size. After mechanical milling, FeCr grains decreased in size more than copper grains due to the ductility of copper grains. The smaller crystals occurred after grinding, and increased the grain boundary zone for further spread of Cr into the Cu. Despite the high sintering process, the high sintering temperature improved the compactness of the alloys, but caused coarsening of the nanoparticles. The mechanical alloying time, reinforcement wt.% and sinter temperature were effective on the micro-hardness of the microstructure.

For a comprehensive microstructural characterization of welds, a scale-bridging analysis of the microstructure is required. It is the only way to identify all microstructural characteristics relevant for the mechanical properties which, in turn, may cover several observation scales. The analytical methods used range from etchings for the macroscopic evaluation of the weld and heat-affected zone to the detection of so-called “local brittle zones” (LBZs) in the micrometre range. This paper will study weld joints in low-alloy steels produced by multi-wire submerged arc welding and electron beam welding. Macro and micro etching as well as electropolishing will be used for microstructural contrasting. Scanning electron microscopy will be performed to identify the finely dispersed carbon-rich secondary phase. Electron backscatter diffraction will enable the identification of so-called martensite/austenite regions (MAs) capable of acting as LBZs.

The best aluminum alloys for construction are those that incorporate copper. However, welding engineers find it difficult to join aluminium and its alloys as a result of cracking. One of the popular methods for joining nonferrous materials, especially aluminum alloys, is friction stir welding (FSW). A tensile strength of 75 % to 85 % of the basic material strength is produced by FSW joints. The majority of studies have documented a reduction in strength as a result of incomplete melting, creating a soft region at the boundary between the thermo – mechanically influenced zone and the stir zone. The current effort has focused on using the shot peening method to reduce the softness at the interface. According to the test findings, the nickel shot-peened joint produced a stronger joint than the traditional FSW joint. The shot-peened joint has gained 7 % additional strength compared to untreated joint.

This paper is a compilation of failure analysis case studies exploring the subject of inadequate heat treatment. As with other papers in this series, the presented failure cases are rather simple and may appear trivial to the experienced failure analyst. The authors can guarantee however, that minor heat treatment errors are committed easily and have a considerable damage potential which may entail heavy financial losses. Therefore, cases of inadequate heat treatment or a complete lack of necessary heat treatment belong by all means in the column Failure Analysis . The metallurgical subject of these failure cases are low-alloy hardenable steels without exception. Common heat treatment processes such as induction hardening, case hardening, nitriding as well as through-hardening and tempering will be touched upon.