A. Raja Annamalai

Effect of heating mode on sinterability of carbonyl iron compacts

Abstract In recent years, microwave processing has gained wide acceptance as a novel method for sintering metal powders. As compared to conventional sintering, microwave sintering provides rapid and volumetric heating involving conversion of electromagnetic energy into thermal energy within the material. This results in finer microstructures, thereby providing improved mechanical properties and quality of the products. This study examines the dependence of densification, microstructure and mechanical properties on the heating mode of Fe–2%Cu and Fe–2%Cu–0·8%C. The powdered compacts were sintered in conventional (radiation mode) and microwave (2·45 GHz, multimode) furnaces at 1120°C in 90N2–10H2 atmosphere, and comparative analysis of the properties was investigated.

Sintering of Tungsten and Tungsten Heavy Alloys of W-Ni-Fe and W-Ni-Cu: A Review

Abstract Tungsten is a refractory metal possessing good mechanical properties of high strength, high yield point, and high resistance to creep. Therefore, tungsten and its alloys are used in many high temperature applications. Due to the high melting point, they are generally processed through powder metallurgy method. The powders are compacted using die pressing or isostatic pressing. The compacts are sintered in a sintering furnace to achieve high density, thereby, making the metal suitable for further processing. This article reviews the recent research findings of consolidating tungsten and its alloys (W–Ni–Fe and W–Ni–Cu), from preparation of powder alloys to sintering of the compact. The advances in sintering are based on the objective of achieving good densification of the metal at lower temperature and at faster rate. The use of microwave sintering and spark plasma sintering techniques resulted in significant reduction in sintering time and producing products of good mechanical properties.

Effect of various sintering methods on microstructures and mechanical properties of titanium and its alloy (Ti–Al–V–X): A review

Titanium having high demand in aircraft industries because of its mechanical properties like high strength to weight ratio, high temperature performance and it’s resistant to corrosion. Therefore, Titanium and its alloys are used in airplane and engine applications. One of the major usages of alloy in the aircraft industries are Titanium alloy. By using Powder Metallurgy, the powder materials are compacted and sintered in the furnace to achieve high densities for the further process of the samples. In this paper reviews the various research investigations of Titanium and its alloy (Ti–% Al–% V–% X alloy), to optimize the microstructure and mechanical properties by various sintering methods like Conventional, Spark plasma and Microwave sintering techniques. From this the major advantages in the Spark plasma sintering tend to reduce the sintering time with high temperatures, achieving higher densities and improved microstructures tends to improve the mechanical properties of the material.

Activated sintering of tungsten alloys through conventional and spark plasma sintering process

ABSTRACT The sintering temperature of pure tungsten can be reduced through the addition of small amounts of transition elements. The present study deals with the activated sintering of tungsten with 1.0 wt% additions of copper, cobalt, molybdenum, iron and nickel using the spark plasma sintering (SPS) technique. The alloys were sintered at 1200°C and the mechanical properties and microstructures were compared with those of conventionally sintered alloys, sintered under vacuum condition. The high-rate sintering of SPS has led to an overall reduction in process time and also to a better densification of alloys compared with the conventional sintering process. In both the processes, nickel addition is found to be the best activator, followed by cobalt, iron, molybdenum and copper. The addition of copper and molybdenum showed only a meager increase in the relative density. The alloys, with nickel, cobalt and iron additions, sintered through the SPS process offered much higher density compared with the conventionally sintered alloys. The highest density is observed for the nickel-doped tungsten alloy, which is found to be around 90% of the theoretical density. The microhardness of the sintered alloys is found to depend on its sintered density.

Effect of heating mode and electrochemical response on austenitic and ferritic stainless steels

Abstract Powder metallurgical (P/M) processing has the main advantage of making near net shape products. Nowadays, in automobile industries, stainless steels have become the most promising material owing to their good corrosion resistance. In the current study, 316L and 434L stainless steel powders were sintered using microwave and conventional methods through powder metallurgy route. The effects of sintering modes on the microstructure, mechanical properties and corrosion responses of 316L and 434L stainless steel composites are investigated in detail. The results showed that the sample prepared through microwave sintering route exhibited significantly superior densification, higher hardness and better corrosion resistance as compared to the conventionally processed counterpart. On the whole, 316L composites showed better corrosion resistance than 434L stainless steels.

Effect of Heating Mode on Sinterability of Fe-Ni Steels

Abstract The present study examines the effect of heating mode on the densification, microstructure, and mechanical properties of iron-nickel steel with graphite and phosphorus addition. The compacts were sintered in conventional (radiatively-heated) and microwave (2.45 GHz, multimode) furnaces at 1120°C for 1 hour in forming gas (dissociated ammonia atmosphere, 95% N2-5% H2). The experimental results show that microwave sintered alloy has better properties compared with the conventionally sintered counterparts. Detailed analyses by using optical microscopy and scanning electron microscopy (SEM) reveal that microwave sintered sample has finer microstructure. SEM examination of the fractured surfaces indicate that a mixed mode fracture containing both, ductile and brittle types, is present in microwave sintered alloy, in contrast with the brittle fracture only in conventional sintered counterpart.

Effect of heating mode and Y2O3 addition on electrochemical response on austenitic and ferritic stainless steels

Abstract The present study compares the effect of Y2O3 addition and heating mode on the electrochemical response on austenitic (316L) and ferritic (434L) stainless steel during solid state sintering. Up to 12 vol.-%Y2O3 was added to 316L and 434L stainless steel. The compacts were sintered at 1350°C for 60 min. The sintered samples were characterised for their density and hardness. The effect of heating mode and Y2O3 addition on the microstructural evolution and electrochemical (corrosion) response for the microwave sintered samples are compared with conventionally sintered samples. The density of stainless steel samples sintered through the microwave sintering was higher than that of conventional sintering.

Microstructural Evolution of Iron Based Alloys Produced by Spark Plasma Sintering Method

The effect of alloying additions, such as copper, carbon, and molybdenum with carbonyl iron powder, on the densification behavior, microstructural evolution, and mechanical properties of spark plasma sintered (SPS) compacts have been investigated in this work. The sintering temperature, pressure, and time during SPS were 1120°C, 30 MPa, and 5 min, respectively. Fe–2Cu–0.8C–0.6Mo was found to exhibit the highest density, hardness, and also tensile strength among all the compositions attempted. The microstructural examination of fractured surfaces of the sintered samples revealed the evidence of a mixed mode of fracture in all the alloy compositions.

Effect of TiC Addition and Heating Mode on the Electrochemical Response of Powder Metallurgy Processed Corrosion-Resistant Austenitic and Ferritic Steels

Austenitic steel 316L and ferritic steel 434L produced by sintering of atomized powders with additions of different volume fractions (0, 4, 8, and 12 vol.%) of titanium carbide particles in microwave and conventional furnaces are studied. The microwave heating results in more intense densification, hardening, higher corrosion resistance, and grain refinement as compared to sintering in the conventional furnace. Steel 316L with 4 vol.% TiC sintered in the microwave furnace exhibits the highest corrosion resistance.

Influence of sintering temperature on mechanical properties of spark plasma sintered pre-alloyed Ti-6Al-4 V powder

Abstract Spark plasma sintering provides faster heating that can create fully, or near fully, dense samples without significant grain growth. In this study, pre-alloyed Ti-6Al-4 V powder compact samples produced through field assisted sintering in a spark plasma sintering machine are compared as a function of consolidation temperature. The effect of sintering temperature on the densification mechanism, microstructural evolution and mechanical properties of spark plasma sintered Ti-6Al-4 V alloy compacts was investigated in detail. The compact, sintered at 1100 °C, exhibited near net density, highest hardness and strength as compared to the other compacts processed at a temperature lower than 1100 °C.