**1. Introduction**

Titanium alloys are widely applied in environments susceptible to erosion, including blades, turbines, and desalination pipeline [1]. Among them, Ti-6Al-4V is the most representative among the α + β titanium alloys [2,3], which possesses excellent specific strength, fracture toughness, corrosion resistance, and bio-compatibility [4]. However, its low thermal conductivity and high reactivity features, which result in its poor machinability characteristics, make it difficult to undertake further exploitation [5]. In addition, specific heat treatment operations are generally required due to the heat hardening phenomena during the cutting process. Additive manufacturing (AM) technology possesses grea<sup>t</sup> characteristics as a new manufacturing technique that is able to lower the cost and reduce energy consumption as well, solving current problems in the fabrication of Ti-6Al-4V and producing a near net shape component [6–8]. Powder bed fusion (PBF) process which uses metal powders as a raw material is a type of additive manufacturing (AM) technology. During PBF, metal powders are melted in a specified area with a high-energy laser beam, then it is rapidly solidified at a high cooling rate [9–13], resulting in its possessing the martensitic α' phases, which differs from the classical α + β phase structure. In the meantime, the phase transformation takes place when the material is heated.

Erosion wear often results in the failure of mechanical devices and components. Therefore, it is necessary to study the erosion wear phenomenon. However, there are a significant number of research articles on the mechanical properties of PBF Ti-6Al-4V [14,15], but few on the erosion wear. And the little research about the wear of titanium alloys, most of them focusing on water droplet erosion [16–19], not on solid particle erosion. The particle erosion articles had also mainly focused on erosion resistance [20–22], instead of the particle erosion-induced phase transformation. According to our previous researches [23,24], particle erosion wear is able to induce phase transformation and affects the erosion rate. Therefore, we want to clarify the erosion-induced phase transformation mechanism

and its effect on the tensile mechanical properties in this study. In this part, erosion particles were used to positively erode the as-PBF Ti-6Al-4V and the heat-treated specimens at a 90◦ impact angle. The results have significant reference value for relevant industry applications.
