Mechanical Properties and Corrosion Resistance of Borosintered Distaloy Steels
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JMEPEG https://doi.org/10.1007/s11665-020-05186-x
Mechanical Properties and Corrosion Resistance of Borosintered Distaloy Steels Selvin Turgut and Ali Gu¨nen (Submitted May 11, 2020; in revised form August 22, 2020; Accepted September 13, 2020) Distaloy SA is a sponge iron powder (nominal composition: Fe-1.75Ni-1.5Cu-0.5Mo) widely used in the production of powder metallurgy (P/M) parts in the automotive industry. In this study, Distaloy SA powders were sintered in two different atmospheres, one consisting of pure Ar gas (traditional sintering) and the other consisting of a mixture of 90 wt.% B4C and 10 wt.% NaBF4 powders (borosintering). To investigate the effects of the different sintering atmospheres, the P/M samples were characterized using density measurements, surface roughness tests, scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, microhardness measurements, nanoindentation experiments, wear tests and corrosion tests. On the surface of the borosintered samples, a 160-325 lm thick double-phase FeB + Fe2B boride layer was formed. The hardness (1405-1688 HV) and elastic modulus (122.21-162.42 GPa) of the surface were significantly improved with the borosintering treatment compared to conventional sintering (215-250 HV, 63.28-94.86 GPa). Borosintering also provided low friction coefficient values and an increased wear resistance compared to conventional sintering. A significant increase in corrosion resistance was also observed with the borosintering treatment in three different solutions. The corrosion rates of both sintered and borosintered samples were ranked as NaCl < HCl < H2SO4. The borosintered samples displayed superior corrosion resistance compared to the sintered samples, especially in the acid solutions. The results of this study show that significant cost savings can be achieved by combining the boriding and sintering treatments in a single borosintering process. Keywords
boriding, corrosion, powder metallurgy, sintering, wear
1. Introduction Powder metallurgy (P/M) is a densification process in which solid components are fabricated by the pressing and subsequent heating (sintering) of powders (Ref 1, 2). Materials that cannot be made by conventional casting technologies or materials with limited formability can often be produced by cost-efficient P/M techniques (Ref 2, 3). Initially favored for its low cost, P/M is preferred today for features such as high-dimensional precision and homogeneity that it can offer in the product (Ref 2-7). Examples of P/M parts include filters, electrical fittings, watches, tungsten lamp filaments, gears, self-lubricating bearings, electrical contacts, armor-piercing bullets, aircraft brake pads, jet engine components, welding electrodes, biomedical prostheses, nuclear power plant components and circuit boards (Ref 2, 4, 8-10). The surface quality of a material produced by P/M is generally good and dimensions are precise. The composition of a P/M product can be tailored by changing the constituents (or fraction of constituents) in the po
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