Effect of metallurgical defect and phase transition on geometric accuracy and wear resistance of iron-based parts fabric
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systematic analysis of effect of metallurgical defect and phase transition on geometric accuracy and wear resistance of iron-based parts fabricated by selective laser melting was conducted. By composition optimization of alloying elements, the desirable martensitic structure was directly obtained based on high-speed laser induction and the content of retained austenite was observed to be different under various laser parameters. Using an optimized scan speed of 1600 mm/s could lead to the highest densification level of 99.24% and the lowest content of retained austenite of 3.5%, hence acquiring a considerably high Rockwell hardness of 61.9 HRC, a reduced coefficient of friction of 0.40, and wear rate of 1.8 105 mm3/N m. A thorough investigation of dimension offset due to martensite transformation in conjunction with theoretical calculation was performed. Lower top surface roughness (5.25 lm) and reduced side roughness (13.84 lm) were achieved at the optimized scan speed of 1600 mm/s.
I. INTRODUCTION
Fabrication of tailor-made products and complexshaped artifacts using traditional methods, such as casting and powder metallurgy, generally is a time-consuming process in a multiple step route.1 Before a tool is put into use, it requires tedious heat treatment procedures, like quenching and tempering, to meet the service demand. These operations are usually not only of low efficiency and high cost, but difficult to guarantee quality. Therefore, it is profoundly significant to find out an available manufacturing approach avoiding undesired follow up process but still obtaining outstanding mechanical properties. In recent years, additive manufacturing (AM), as presently one of the fast-developing advanced manufacturing techniques in the 21st century, emerged and has demonstrated promising application perspective with the introduction of several advanced energy carriers, such as the laser beam, electronic beam, and plasma jet.2 Selective laser sintering (SLS) and selective laser melting (SLM) are currently regarded as the two most versatile AM processes.3 Due to the additive nature, threedimensional (3D) parts with extremely complex shape
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.132 J. Mater. Res., Vol. 31, No. 10, May 28, 2016
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can be built directly from powders. Laser beam is used to selectively consolidate prespread powders in a layerby-layer method. The laser scanning is controlled by a computer and each processed layer corresponds to a two-dimensional (2D) cross-section of the mathematically sliced computer-aided design model of the part.4 The rapid tooling using SLS, which is based on a semisolid consolidation mechanism, has been proved to be unsatisfied, due to the material limitation, considerably high porosity and severe balling phenomenon caused by the limited wettability of liquid.5 In comparison, SLM has large flexibility in feedstock and extremely complexshaped parts
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