Improved mechanical properties and microstructural development of microwave sintered copper and nickel steel PM parts

Abstract

The application of microwave technology to a diverse range of materials and processes has resulted in a wide spectrum of materials that are commercially processed using microwaves, from the heating of food to the vulcanisation of rubber to the sintering of specialty ceramics. Microwave sintering of elemental or alloy metal powders has gained significance in recent times as a novel processing method since it offers many advantages over the conventional sintering method. Despite substantial R&D investment in this area in the past two decades, no competitive microwave technology has yet emerged for powder metallurgy (PM) sintering. In sharp contrast, because it is 'obvious' that microwaves are reflected by metals, it is not uncommon to be unable to locate many journal papers or literature, wherein metal powders have been sintered in a microwave field. This paper reports the improved mechanical properties and microstructural development of microwave sintered copper and nickel steel PM parts as compared with that obtained using conventional sintering technique.The paper describes the fabrication details of the FC-0208 and FN-0208 composition steel PM parts, and the in house modified commercial microwave oven used for sintering. Microwave sintering resulted in higher sintered density and improved mechanical properties for both Cu and Ni steel PM parts as compared with that processed using conventional sintering under identical conditions. The improved mechanical properties can be attributed primarily to more uniform distribution of the alloying elements, which resulted in greater material homogeneity at the nano-and microlevels as revealed by the Cu and Fe X-ray maps using high spatial resolution scanning transmission electron microscopy (STEM). The optical micrographs of both the etched and unetched samples clearly showed development of novel sintered microstructures having distinct characteristics for the porosity distributions: smooth and rounded pores with low stress concentration regions for microwave sintering as against sharp, triangular and wedge shaped pores with high stress concentration regions for conventional sintering.

A Unit Cell Approach to Model and Characterize the Metal Powders and Metal-Dielectric Composites at Microwave Frequencies

“…Now, once the value of t local is obtained using (9), the value of β can be obtained using (10), and this value of computed β along with the value of z computed using (11) can be employed to determine the value of µ * r using (6). The value of * r of the test specimen can finally be calculated using (4) as the value of β and µ * r is already determined.…”

“…The microwave energy has traditionally been used to heat lossy dielectrics such as food items for home appliances, and certain class of polymers and composites for various industrial applications [3][4][5]. However, recently, there has also been lot of interest to explore the use of microwave technology for sintering of metal powders after a study showing the absorption of microwaves by metal powders under certain conditions [6][7][8], and it has been reported that the microwave sintering could provide improved mechanical properties along with the finer micro structures [9] as compared to the conventional sintering. As the bulk metals reflect microwaves, hence the basis of microwave heating of metal powders can only be understood by realization of the basic fact that the metal powders should be treated as lossy dielectrics having mixtures of metal particles embedded in a host dielectric medium which may be considered as air for a very simple case.…”

Microwave Processing of Metallic Glass/Polymer Composite in a Separated H-Field

“…As good electrical conductors, bulk metals can not be well heated up because microwaves interaction with metals is restricted to its surface, but fine metal powders may be couple with microwaves at room temperature by Joule heating and magnetic-induced effects. Now a variety of metallic materials have been successfully sintered and processed in a pure microwave system or a hybrid heating system in which an external microwave susceptor is used [Anklekar, et al, 2005;Gedevanishvili, et al, 1999]. Although the mechanisms of microwave heating have not been fully understood until now, there is still an increasing interest in microwave processing of various materials, especially new materials with potential applications.…”

Comparative analysis of niobium and vanadium carbide efficiency in the high energy mechanical milling of aluminum bronze alloy

“…Then pure metals or intermetallics are compacted in a die at room temperature and for the sintering of the consolidated powders for densification, a furnace is used (NAWATHE et. al, 2009;ANKLEKAR et. al, 2005;SURYANARAYANA, 2001).…”