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M300 maraging steel was fabricated by selective laser melting (SLM), and the effect of heat treatments on the corrosion and stress corrosion resistance of the alloy was evaluated in 3.5% NaCl solution. The microstructure of the alloy in the solution-treated and aged condition is typical of lath martensitic structure along with metallurgical defects typical of SLM-processed material. The results indicated that M300 steel processed by SLM is highly susceptible to stress corrosion cracking (SCC). The fracture morphology of the samples exhibited brittle intergranular cracking along with ductile cracking features in NaCl. HIP treatment after SLM and before solution treatment and aging improved the SCC resistance of the alloy in terms of marginal increase in elongation in NaCl solution. However, this treatment could not completely eliminate the SCC susceptibility of the maraging steel in NaCl solution. The SCC susceptibility of M300 maraging steel processed by SLM can be attributed to the presence of defects such as pores which assisted the early initiation of cracks and the resultant intergranular (IGC) failure. The defects were considerably healed by subjecting the SLM-processed alloy to HIP treatment, thus improving the SCC resistance. In addition to the reduction in pore density, the increased austenite content present in the alloy after heat treatment played significant role toward improving the corrosion resistance of the as-printed M300 steel.

Oxide dispersion strengthening is an effective method to improve the high-temperature mechanical properties of the alloys in which various reinforcements are added in the alloy matrix by mechanical milling and consolidating the mixture by different techniques like hot pressing, hot isostatic pressing and spark plasma sintering. This work presents the development of IN 718 ODS alloy by dispersing yttria in IN 718, which has improved mechanical properties at high temperatures. Yttria powder was added to IN 718 alloy powder in different weight fractions of 0.25, 0.5 and 1% and mechanically milled. The composite powders were consolidated by hot pressing and hot isostatic pressing (HIP). A small fraction of isolated porosities in the matrix was observed in hot-pressed samples which caused degradation of the mechanical properties. Percentage of porosities increased with the increase in yttria content. The hot-pressed samples were HIPed to heal the porosities. 0.5 wt% yttria-dispersed Inconel 718 hot-pressed compact exhibited better properties at 850 °C and showed 50 MPa improvement in ultimate compressive strength compared to Inconel 718 alloy.

Hot isostatic pressing (HIPping) technology is used for healing the casting defects for aerospace applications. Castings used for aerospace applications like turbo-pumps need to meet very stringent quality requirements. Complexity of the castings used in these applications, makes it difficult to meet the quality requirements in all the areas. Defects like gas holes, shrinkages, cavities etc. may occur in few locations and need to be repaired by welding or healed by HIPping. In the present study, we attempted to simulate the defect healing capability of HIP in a systematic manner. Artificial defects were created in Austenite-Martensite grade stainless steel cast rod. These rods were then subjected to HIP prcoss cycle at 1150 °C and at a pressure of 1620 bar. Healing of the defects was ensured through X-ray radiography. Detailed microstructural analysis using optical metallography and scanning electron microscopy (SEM) with EDX was carried out before and after HIPping, to understand the defect healing mechanisms. These results are discussed in detail here.

Rheocasting refers to a process in which a liquid metal is vigorously agitated during initial stage of solidification to produce globular semisolid slurry which remains highly fluid. This slurry is directly fed into any shaping operation to obtain SSM parts. Rheocasting is an energy saving as well as cost saving, good surface finish and negligible porosity for a specialized casting, in which heating step of thixocasting is completely eliminated. Rheocasting also offers shot size flexibility and amenable for processing of wrought alloys and metal matrix composites, which are otherwise difficult to process by thixocasting route. A slurry with globular shape of the solid phase particles and hence injected directly into the die. In the present development, Al base thin wall components for electronic packaging applications were produced by rheocasting process. The paper presents the die designing aspects, optimization of rheocasting process parameters to achieve the sound casting and mechanical property. Thin walled Al-Alloy components lot was realized by the novel processing technology, meeting dimensional accuracy, desired microstructure, mechanical property, value for high integrity component needed for space applications.

Silver-Graphite composites are attractive materials for electro-mechanical devices to provide noise free rotation between mating surfaces with minimum contact voltage drop. In the present study, the composite was processed through Powder Metallurgy (P/M) route considering that the constituent elements have divergent physical properties without any metallurgical bond between them. The developed composites were evaluated for hardness, electrical resistivity, contact voltage and density. This paper presents a correlation between hardness and electrical resistivity against volume fraction of graphite added, through linear regression which has clearly indicated that the said properties of the composites are highly dependent on the volume fraction of graphite. The hardness and electrical resistivity of the composites were found to obey the relations given below (i) Log H=1.522 + 1.667 Log (1-fg), (ii) 32.36 Log (ρ0/ρ) =1 + 83.74 Log (1-fg), where H is hardness of composites, ρ0 is electrical resistivity of pure silver, ρ is electrical resistivity of composites and fg is the volume fraction of graphite.