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Purpose The purpose of this paper is to investigate effects of layer thickness on densification, surface morphology, microstructure and mechanical and corrosion properties of 420 stainless steel fabricated by laser-powder bed fusion (L-PBF). Design/methodology/approach Standard specimens were printed at layer thickness of 10, 20 and 30 µm to characterize Archimedes density, surface roughness, tensile strength, elongation, hardness, microstructural phases and corrosion performance in the as-printed and heat-treated condition. Findings Archimedes density slightly increased from 7.67 ± 0.02 to 7.70 ± 0.02g/cm3 and notably decreased to 7.35 ± 0.05 g/cm3 as the layer thickness was changed from 20 µm to 10 and 30 µm, respectively. The sensitivity to layer thickness variation was also evident in properties, the ultimate tensile strength of as-printed parts increased from 1050 ± 25 MPa to 1130 ± 35 MPa and decreased to 760 ± 35 MPa, elongation increased from 2.5 ± 0.2% to 2.8 ± 0.3% and decreased to 1.5 ± 0.2, and hardness increased from 55 ± 1 HRC to 57 ± 1 HRC and decreased to 51 ± 1 HRC, respectively. Following heat treatment, the ultimate tensile strength and elongation improved but the general trends of effects of layer thickness remained the same. Practical implications Properties obtained by L-PBF are superior to reported properties of 420 stainless steel fabricated by metal injection molding and comparable to wrought properties. Originality/value This study successfully the sensitivity of mechanical and corrosion properties of the as-printed and heat-treated parts to not only physical density but also microstructure (martensite content and tempering), as a result of changing the layer thickness. This manuscript also demonstrates porosity evolution as a combination of reduced energy flux and lower packing density for parts processed at an increasing layer thickness.

Niobium (Nb) and molybdenum (Mo) are conventionally added to stainless steels to improve their mechanical and corrosion properties. However, the effects of Nb and Mo addition on the processing and properties in laser-powder bed fusion (L-PBF) have not been well investigated, especially in the context of 420 stainless steel. In this study, 420 stainless steel pre-alloyed with Nb (1.2 wt.%) and Mo (0.57 wt.%) was processed by L-PBF and characterized in terms of its physical, mechanical and corrosion properties as well as microstructure. The addition of Nb and Mo did not significantly affect the densification of 420 stainless steel when printed over an energy range of 28–75 J/mm3 and a maximum density of 99.3 ± 0.02% theoretical at 63 J/mm3 was achieved. In mechanical tests, L-PBF 420 stainless steel specimens exhibited higher mechanical properties in the presence of Nb and Mo. After heat treatment, the UTS of 420 stainless steel with Nb and Mo improved to 1750 ± 30 MPa and elongation to 9.0 ± 0.2%, much higher than previously reported properties achieved in L-PBF and exceeding wrought 420 stainless steel. The tempering of martensite phases as well as the presence of nanoscale NbC were found to correlate with improved mechanical properties. In electrochemical tests, 420 stainless steel exhibited slightly better corrosion properties with the addition of Nb and Mo.

In this study, we report the mechanical properties, microstructure and corrosion behavior 99+ % dense 420 stainless steel parts fabricated by laser-powder bed fusion (L-PBF). As-printed L-PBF parts exhibited an ultimate tensile strength of 1050 ± 25 MPa, yield strength of 700 ± 15 MPa, an elongation of 2.5 ± 0.2% and a hardness of HRC 55 ± 1. After the heat treatment operation at 315 °C, the ultimate tensile strength improved significantly to 1520 ± 30 MPa, yield strength increased to 950 ± 20 MPa, and elongation increased to 6.3 ± 0.2% respectively whereas hardness remained at HRC 53 ± 1. These properties are higher than previously reported literature values for 420 stainless steel fabricated by L-PBF, metal injection molding and powder metallurgy routes. The microstructure indicated a mixture of martensite and retained austenite phases in the as-printed parts. After heat treatment, the microstructure was richer in tempered martensitic laths that is consistent with the enhancement of ultimate tensile strength, yield strength, and elongation without appreciable change in hardness. The corrosion behavior of the as-printed L-PBF parts exhibited a corrosion current of 2.85 ± 0.4 mA.cm−2, a polarization resistance of 17,100 ± 520 Ω.cm−2 and a corrosion rate of 28 ± 2 μm/year which were comparable to the corrosion properties of wrought 420 stainless steel. A significant increase in pitting potential (170 mV) was obtained after the heat treatment.

The effects of powder characteristics (powder shape, size and type) and processing conditions (laser power and scanning speed) on the mechanical properties and microstructures of laser powder bed fusion (L-PBF) 17-4 PH stainless steel were studied using four types of powders. The % theoretical density, ultimate tensile strength, hardness of L-PBF parts are sensitive to energy density and starting powder shape, size and type. The density and mechanical properties of both water and gas-atomized powders increased with increased energy density. The gas-atomized (D50 = 13 μm) powders which are spherical in shape and water-atomized (D50 = 17 μm) powders of high tap density produced low-porosity and high-density (~97% density) L-PBF parts at low energy densities of 64 and 80 J/mm3. The increase in energy density to 104 J/mm3 resulted in high dense (97 ± 0.5%) water- and gas-atomized powders L-PBF parts. However, even at a high % theoretical density (97 ± 1%), the properties of L-PBF parts varied over a relatively large range (UTS: 500–1100 MPa; hardness: 25–39 HRC; elongation: 10–25%). This large variation in mechanical properties could be attributed the martensite and austenite phase as well as grain size in the L-PBF parts. Furthermore, the martensite and austenite phase content and of the L-PBF parts were also sensitive to the energy density and starting powder type.

In the present work, the friction and wear properties of Polypropylene (PP) based composites filled with Hydroxyapatite (HA) particles were studied. Fillers contents in the PP were 10, 20, and 30 wt%. The effects of hydroxyapatite ratio on the water absorption, friction and wear properties of the polymer composites is presented. The result showed that the addition of HA to the composite changed the water absorption, friction coefficient and wear rate.