Effect of process parameters on tribological performance of 316L stainless steel parts fabricated by selective laser melting

doi:10.1016/j.mfglet.2018.04.003

Manufacturing Letters

Volume 16, April 2018, Pages 36-39

https://doi.org/10.1016/j.mfglet.2018.04.003 Get rights and content

Abstract

Selective laser melting (SLM) is an additive manufacturing technique based on metallic powders that are melted by the energy of laser with a layer build-up technique. This paper investigates the effect of process parameters on tribological performance of 316L stainless steel samples made by SLM. Rectangular samples were produced using SLM at different laser powers and along different build-up directions. Sliding wear tests were conducted under two different normal loads at a constant frequency of 4 Hz in ambient temperature. A scanning electron microscope was used for observing the microstructures and wear tracks. The results showed that lower laser powers resulted in samples with lower hardness and densities and lack of fusion at melt pools boundaries. However, the effects of laser power and build-up direction on coefficient of friction (COF) and wear rate are not significant. At higher contact pressures, wear rate was higher, but COF was not affected remarkably. The findings suggest that further study of process parameters, material properties and performance can advance tribological applications of SLM parts.

Introduction

Selective laser melting (SLM) is one of the most popular metal additive manufacturing (AM) technologies, which builds a part by selectively melting powdered feedstock layer by layer [1]. With many advantages, such as the high flexibility of product’s shape, short process time, and various materials availability, SLM has been a very attractive technique. Due to its distinctive processing philosophy, the quality of production is strongly related to SLM processing parameters (e.g. laser power, build-up direction, scan speed, and hatch distance).

Various studies have been conducted on the effects of processing parameters on SLMed parts; however, little work has been done in the field of tribological properties. Tribology plays an important role in engineering and characterising the tribological performance of materials is crucial [2]. Previous studies indicated that processing parameters such as laser power, point distance or scan speed have strong effects on density of parts produced by SLM and the presence of porosity leads to a decrease in mechanical strength [3]. SEM images showed large-sized irregular-shaped pores were distributed in microstructure of components made by SLM [4]. It was also reported that laser power is one of the most influential process parameters; and with decrease in the laser power, the tensile properties deteriorate due to the increase of porosity [5]. Some authors illustrated that with optimized parameters, SLM process is capable of producing highly dense (98–99.5% of theoretical density) parts [6], [7], [8].

A positive linear correlation between volume percentage of porosity and wear rate was found by Sun et al. [9] for SLMed samples. However, more studies on processing parameter are required to deal with reducing porosity. It has been shown by Gu et al. [1] that insufficient densification and coarsened grains which caused by unoptimized scanning speed limit the hardness of SLMed pure Ti parts. By adjusting linear energy densities, Gu et al. [1] found that wear rate and COF followed similar trend with hardness performance. Nevertheless, to the best of the author’s knowledge, there are still no related studies focusing on inherent relationship between processing parameters and wear behaviour of SS 316L material and a systematic approach to investigate the effect of SLM process parameters on tribological behaviour is still missing. The objective of this study is therefore to investigate the sliding wear behaviours of SS 316L parts fabricated by SLM with different laser powers and building orientations.

Section snippets

Material and methods

A commercial SLM machine (Renishaw AM400) equipped with an inert gas and vacuum system was used to produce the samples with 316L stainless steel powder (Renishaw 316L-0407) with a particle size of 15–45 µm. The machine uses a fibre laser with a wavelength of 1070 nm, whose beam diameter at the focal point is 70 µm. Test samples were made by four different laser powers of 100 W, 150 W, 200 W and 300 W and three different build-up directions. A hatch distance of 110 µm and a layer thickness of

Results and discussion

Table 1 shows the surface roughness, hardness, density and porosity of samples made by different laser powers and with different built-up directions. The porosity was estimated based on the measured density, $p = 1 - ρ / ρ_{th}$ , where $p$ is the porosity, $ρ$ is the measured density, and $ρ_{th}$ is the theoretical density of the material (7950 kg/m³). Hardness test results showed that it increases by the increasing laser power, and hardness values for 200 W and 300 W laser powers are almost the same. SLM

Conclusions

A linear reciprocating tribometer was used to perform dry sliding wear tests on 316L stainless steel samples made by SLM with different laser powers and build-up directions. The results showed that laser powers and build-up directions do not have a remarkable influence on COF and wear rate. With lower laser powers, samples with more pores and lower hardness were produced. This should indicate a high wear rate, but the test results showed the specimens from lower laser powers have a lower or

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Densification behavior, microstructure evolution, and wear performance of selective laser melting processed commercially pure titanium
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E. Liverani et al.
Effect of selective laser melting (SLM) process parameters on microstructure and mechanical properties of 316L austenitic stainless steel
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H. Chen et al.
Effect of metallurgical defect and phase transition on geometric accuracy and wear resistance of iron-based parts fabricated by selective laser melting
J Mater Res
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Top surface and side roughness of Inconel 625 parts processed using selective laser melting
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Effect of process parameters on tribological performance of 316L stainless steel parts fabricated by selective laser melting

Abstract

Introduction

Section snippets

Material and methods

Results and discussion

Conclusions

Acta Mater

J Mater Process Technol

Effect of metallurgical defect and phase transition on geometric accuracy and wear resistance of iron-based parts fabricated by selective laser melting

J Mater Res

Top surface and side roughness of Inconel 625 parts processed using selective laser melting

Rapid Prototyping J