Additively manufactured SiC-reinforced stainless steel with excellent strength and wear resistance

Highlights

• The SiC reinforced 316L reaches a high tensile strength of 1.3 GPa.

• Achieved strength and wear resistance are at the highest level among literature.

• Strengthening mechanisms are illustrated and discussed in details.

Abstract

Additive manufacturing enables in-situ alloying of multi-component materials for the development of novel and high-performance materials. Here laser powder bed fusion (LPBF) of SiC-reinforced 316L stainless steels metallic matrix composites (MMCs) for improved strength and wear resistance were investigated. The densification behaviour, microstructural evolution, crystallographic orientation and properties of the LPBF-processed MMCs with different SiC contents were systematically investigated. The formation mechanisms of pores and cracks are discussed. Microstructural observations reveal that the microstructure changes from equiaxed to dendritic with increasing SiC are related to the different temperature gradient and solidification rates. The SiC addition affects crystallographic orientation and causes grain refinement to 316L. In addition, micron SiC particles are refined to nano-scale after laser processing, which induces massive dislocations in the 316L matrix. The strength and tribological properties of 316L are significantly improved by SiC addition, in which the 9 vol% SiC reinforced MMC reaches a high tensile strength of about 1.3 GPa, together with a low wear rate of 0.77 × 10⁻⁵ mm³/Nm. The achieved strength and wear resistance are at the highest level among literature, and the underlying strengthening mechanisms are elucidated.

Introduction

Laser powder bed fusion (LPBF) is a promising powder-based additive manufacturing (AM) technique, which can produce parts with high dimension precision, complex geometry and desired performance through selectively melting of metal powders by high-energy laser beam [1]. LPBF offers unique advantages in materials development from design concept to large volume production due to the short developing cycle and lead time, high material and cost efficiencies. Furthermore, the fast cooling rate can result in refinement grain and tailored microstructure, improving the mechanical properties compared with the conventionally manufactured parts [2].

In-situ formation of metallic matrix composites (MMCs) via laser AM processing ceramic particles reinforced metallic matrix is widely used to improve the comprehensive mechanical properties of metals, which takes advantage of the high hardness and wear resistance of ceramics, along with the ductility of the metallic matrix. LPBF of MMCs for improved mechanical or tribological properties of steels using different reinforcements has been intensively investigated recently. AlMangour et al. [3] focused on the microstructure evolution and strengthening mechanism of micro-TiC and nano-TiC reinforced 316L stainless steel. The results demonstrated that the improved compressive yield strength mainly originated from the effect of grain boundary strengthening and Orowan strengthening. The grain boundary strengthening comes from grain refinement as it increased the boundary density, while the Orowan strengthening originates from the interaction between dislocations and the reinforcements, in which reinforcements pin the dislocation, and Orowan bowing is necessary for dislocations to bypass [4]. Zhang et al. [5] successfully fabricated TiC reinforced AISI 420 composites using LPBF, which achieves a better mechanical property compared with the AISI 420 steel, due to the strengthening effect from the well-distributed Ti-based ring-like structure. Han et al. [6] achieved the balance between the strength (738 MPa) and ductility (38%) of LPBF-fabricated single-layer graphene nano-platelets (GNPs) reinforced 316L, which attributed to the combination of precipitation hardening, grain refinement, and load transfer strengthening. Ghayoor et al. [7] successfully fabricated oxide dispersion strengthened 304L stainless by LPBF, achieving a high strength (700 MPa) and ductility of 32%. Additionally, the MMCs are proven to increase the laser absorption of singular metal powders [8], stabilise the melt pool [9], [10], improve densification behaviour [11], and enhance tribological performance [12].

The LPBF-processed 316L stainless steel is widely applied in automotive [13], aerospace [14] and biomedical [15], etc., due to the good ductility, high strength and outstanding corrosion resistance. Nevertheless, there still exists enormous challenges when facing severe working conditions due to the low hardness and poor wear resistance, which prohibits its widespread applications [16]. For instance, the 316L components are prone to fail when being subjected to heavy loads or high wear working conditions. The above literature about LPBF of ceramics reinforced steels shed light on further improving the strength and wear resistance via proper reinforcements.

SiC particles with low density, high hardness and excellent wear resistance were widely used as the reinforcing materials [9], [17], [18]. The SiC particles are proven to be the ideal reinforcing particle in steels due to the good wettability with iron [19] and the higher laser absorption than steels will undoubtedly contribute to good formability [20]. Gu et al. [21] fabricated Al4SiC4 + SiC hybrid reinforced Al matrix composites with nearly full densification and enhanced wear resistance due to the improved reinforcement/matrix wettability caused by the fine SiC particles. Nevertheless, relatively few researches concerning SiC reinforced 316L metallic matrix composites and lack of systematical investigations on the microstructure evolution, grain orientation, tribological and mechanical properties as a function of SiC content.

In this study, SiC reinforced 316L metallic matrix composites were processed by LPBF. The effects of SiC on the densification behaviour, microstructure evolution, crystallographic orientation, mechanical and tribological properties of the LPBFed MMCs were systematically investigated. The achieved strength and wear resistance are at the highest level among literature. The results highlight the capability of in-situ processing MMCs with excellent performance via AM to circumvent the harsh requirements on traditional materials.