# Wear Properties of Sc-Bearing Zr-Based Composite BMG with Nano-CuZr\({}_{2}\) under Lubrication
## 1 Introduction  
Because of BMGs' (bulk metallic glasses) hardness and toughness both being high, they are expected to have superior properties of wear. Literature has pointed out that BMGs have a good wear resistance compared to nanocrystallized materials [1, 2]. By contrast, reports have also indicated that the wear performance of BMGs is considerably inferior to that of the annealed materials [3]. For example, Zr-based BMGs were slid under lubricated and dry frictions for 100 m and 1000 m, respectively. The values of the friction coefficient for the amorphous alloy was slightly lower than that of stainless steel AISI 303 (American Iron and Steel Institute 303) and Ni-200 (commercial pure Ni) under the wear of dry environment. However, this trend was not the mode under lubricated conditions [3]. The Zr\({}_{41}\)Ti\({}_{14}\)Cu\({}_{12.5}\)Ni\({}_{10}\)Be\({}_{22.5}\) BMG-bearing gears have been tested in working life after high-speed rotation testing [4]. The results indicated that the BMG-bearing gear is superior to bearing steel GCr15(YB9-68) under the same conditions. Furthermore, the material was still observed to have a glassy amorphous structure after wear testing. Furthermore, a series of Zr\({}_{48}\)Cu\({}_{45}\)-xA\({}_{77}\)Ag\({}_{X}\) (\(x\) = 0-8 at.%) BMG alloys have been investigated in terms of their dry sliding wear behaviors; the results of wear tests exhibited a significant increase in wear resistance with the addition of Ag in the ternary Zr-Cu-Al system [5]. A Zr\({}_{41.5}\)Ti\({}_{13.8}\)Cu\({}_{12.5}\)Ni\({}_{10}\)Be\({}_{22.5}\) BMG was tested under sliding experiments; an extensive material flow was determined occurring during dry sliding in the environment of either air orvacuum [6]. The friction coefficient in vacuum reduces with an increase in load compared with the environment in air. The sliding wear properties of Cu\({}_{60}\)Zr\({}_{30}\)Ti\({}_{10}\) in various annealing states were compared under dry condition [7]; the wear mechanism involves an easier initiation of crack and crack propagation through the relatively brittle nanocrystalline phases, leading to a nanocrystallized metallic glass exhibiting poor wear performance.  
Nanocrystals dispersed in an amorphous matrix by partial nanocrystallization exhibits effective mechanical properties [8,9], favorable soft magnetism [10,11] and hard magnetism [12,13], and excellent properties of corrosion resistance [14]. Those have not been observed for pure amorphous or pure nanocrystalline alloys. Therefore, the novel structure and technological importance of the partially nanocrystallized intermetallic amorphous matrix materials have attracted considerable attention [15]. However, few research works have focused on the tribological properties of composite BMG or the amorphous matrix with nanocrystal CuZr\({}_{2}\). The intermetallic compound of nano-CuZr\({}_{2}\) is a thermodynamically stable phase. Meanwhile, CuZr\({}_{2}\) is harder than the Zr-based (Zr\({}_{55}\)Cu\({}_{30}\)Al\({}_{10}\)Ni\({}_{5}\))\({}_{99.98}\)Sc\({}_{0.02}\) bulk amorphous matrix. Therefore, it is an attractive bearing and shaft material for industrial application. The current study focused on the lubricated wear properties after a small amount of Sc (scandium) was added to the Zr-based composite BMG. The small amount of Sc addition can enhance the Zr-based (Zr\({}_{55}\)Cu\({}_{30}\)Al\({}_{10}\)Ni\({}_{5}\))\({}_{99.98}\)Sc\({}_{0.02}\) composite BMG glass-forming ability. There are few reports on Sc addition on BMGs. When BMG is used as bearings and shafts, the friction feature of BMG needs to be evaluated comprehensively. In this work, the friction and wear properties of Zr-based BMGs sliding against 440C steel lubricated with industrial oil lubrication was investigated.