Alloy

About: Alloy is a research topic. Over the lifetime, 171884 publications have been published within this topic receiving 1719420 citations. The topic is also known as: alloys.

Effect of laser surface melting on corrosion and wear resistance of a commercial magnesium alloy

Abstract: Among the light metals, Mg and its alloys occupy a prominent position due to its low density, excellent machinability, and high specific strength. However, a relatively poor resistance to corrosion and wear are serious impediments against wider application of Mg alloys. In the present study, an attempt was made to enhance pitting corrosion resistance and microhardness of a commercial Mg alloy, MEZ (Zn 0.5%, Mn 0.1%, Zr 0.1%, rare earth elements 2%, Mg remaining percentage) by laser surface melting. The study included a detailed characterization of laser surface melted zone in terms of microstructure, phase analysis and its correlation with process parameters to optimize the laser processing routine. Mechanical properties like microhardness, wear, and electrochemical properties like pitting corrosion resistance of the surface melted layer were studied in detail. Microhardness of the laser surface melted layer was improved to 85–100 VHN as compared to 35 VHN of the as-received MEZ. Pitting corrosion resistance of the laser surface melted MEZ, significantly improved in a 3.56 wt.% NaCl solution because of grain refinement and redistribution of the intermetallic phases following rapid quenching associated with the process. The wear resistance of laser surface melted layer was also improved as compared to as-received MEZ.

Local Structure and Short-Range Order in a NiCoCr Solid Solution Alloy.

Abstract: Multielement solid solution alloys are intrinsically disordered on the atomic scale, and many of their advanced properties originate from the local structural characteristics. The local structure of a NiCoCr solid solution alloy is measured with x-ray or neutron total scattering and extended x-ray absorption fine structure (EXAFS) techniques. The atomic pair distribution function analysis does not exhibit an observable structural distortion. However, an EXAFS analysis suggests that the Cr atoms are favorably bonded with Ni and Co in the solid solution alloys. This short-range order (SRO) may make an important contribution to the low values of the electrical and thermal conductivities of the Cr-alloyed solid solutions. In addition, an EXAFS analysis of Ni ion irradiated samples reveals that the degree of SRO in NiCoCr alloys is enhanced after irradiation.

Preparation and properties of cast aluminium-ceramic particle composites

Abstract: A casting technique for preparing aluminium-alumina, aluminium-illite and aluminium-silicon carbide particle composites has been developed. The method essentially consists of stirring uncoated but suitably heat-treated ceramic particles of sizes varying from 10 to 200 μm in molten aluminium alloys (above their liquidus temperature) using the vortex method of dispersion of particles, followed by casting of the composite melts. Recoveries and microscopic distribution of variously pretreated ceramic particles in the castings have been reported. Mechanical properties and wear of these composites have been investigated. Ultimate tensile strength (UTS) and hardness of aluminium increased from 75.50 MN m−2 and 27 Brinell hardness number (BHN) to 93.15 MN m−2 and 37 BHN respectively due to additions of 3 wt % alumina particles of 100 μm size. As a contrast, the tensile strength of aluminium-11.8 wt % Si alloy decreased from 156.89 MN m−2 to 122.57 MN m−2 due to the addition of 3 wt % alumina particles of the same size. Adhesive wear rates of aluminium, aluminium-11.8 wt % Si and aluminium-16 wt % Si alloys decreased from 3.62×10−8, 1.75×10−8 and 1.59×10−8 cm3 cm−1 to 2.0×10−8, 0.87×10−8 and 0.70×10−8 cm3 cm−1, respectively, due to the additions of 3 wt % alumina particles.

Effect of standard heat treatment on the microstructure and mechanical properties of hot isostatically pressed superalloy inconel 718

Abstract: Ni–Fe base superalloy, Inconel 718, was processed through powder metallurgy (P/M) hot isostatic pressing (HIP) route. In order to balance the strength and ductility, the HIPed material was given the standard heat treatment, viz. solution treatment at 980 °C for 1 h/water quenched (WQ) to room temperature and a two-step ageing treatment consisting of 720 °C for 8 h/furnace cooling (FC) at 55 °C h−1 to 620 °C and holding at 620 °C for 8 h before air cooling (AC) to room temperature. Optical microscopy and scanning electron microscopy (SEM) studies on the heat treated alloy have shown a homogeneous microstructure with fine grain size (25 μm) along with the presence of prior particle boundary (PPB) networks. Transmission electron microscopy (TEM) on the heat treated material has revealed the presence of oxides, MC carbides and δ-precipitates at the grain boundaries and a uniform precipitation of fine γ″ and γ′ strengthening phases in the matrix. Tensile and stress rupture tests were performed on the heat treated material. While the yield strength (YS) and ultimate tensile strength (UTS) of the HIPed and heat treated alloy at room temperature and 650 °C were comparable to those of conventionally processed wrought IN 718, its ductility was lower. The stress rupture life of the HIPed alloy improved marginally due to heat treatment and met the minimum specification requirement of life hours but the rupture ductility was found to be inferior to that of the wrought material. The fractography of the failed samples has revealed the transgranular ductile mode of fracture in the as-solution treated alloy, while intergranular mode of failure with the decohesion of PPBs occurred more predominantly in the aged condition. This change of fracture mode with ageing treatment shows the ductility dependence on the relative strength of the matrix and PPBs. The TEM studies on the deformed alloy have revealed that the brittle oxides and carbides at the prior particle boundaries coupled with the fine γ″ and γ′-precipitates in the matrix are responsible for low ductility at 650 °C. The investigations of the present study have led to better understanding of the structure–property relationships in HIP+heat treated alloy 718 and suggest that the standard heat treatment recommended for wrought IN 718 is not suitable for HIPed alloy and has to be modified to realise optimum properties.