**1. Introduction**

Selective laser melting (SLM) process is a type of 3D-printer technology used in this study. The process uses metal powder as a raw material, where during the SLM process, metal powders are melted in a specified area with a high-energy laser beam and rapidly solidified at a high cooling rate [1–3].

Ti-6Al-4V is the most representative of the α + β titanium alloys [4,5]. The most common Ti-6Al-4V alloys are cast and forged, and their alloy properties have been widely discussed [6,7]. Many SLM Ti-6Al-4V articles have discussed how process parameters and post treatment interact with microstructure and mechanical properties [8,9]. In this research, the process parameter was fixed. The microstructure of the SLM Ti-6Al-4V contains not only the classical α + β phases but also the martensitic α' phases (low ductility) because of the high cooling rate [10,11]. For industrial applications, achieving improved ductility through an appropriate heat treatment is necessary. Furthermore, Ti-6Al-4V is commercially used in gas turbine engines up to a test temperature of 350 ºC. Industrial applications usually limit Ti-6Al-4V use to 400 ◦C, so high temperature (250–400 ◦C) tensile mechanical properties of SLM Ti-6Al-4V are investigated in this study and a relationship between the high temperature failure behavior and erosion wear characteristics is proposed.

In many industrial applications, erosion wear caused by solid particles results in the failure of mechanical devices and components [12,13]. This study also investigates erosion properties (use Al2O3 particles) between the martensitic α' phase formed by SLM Ti-6Al-4V and the lamellar double α + β phases with heat treatment. Notably, the erosion resistance mechanism was proposed by comparing the relationship between impact angles and erosion rate. According to our previous research studies [14,15], the particle erosion wear is able to induce the phase transformation and affects the erosion rate. The temperature of the

eroded surface is more than 400 ◦C, and the relationship between wear behavior and high temperature tensile properties needs to be clarified [16]. This study is one of the few articles discussing the high temperature strength and particle erosion properties of SLM Ti-6Al-4V alloy. The relevant results have significant reference value for relevant 3D-printer titanium alloys.
