Injection molding is the main process for the mass production of plastic products in the world. Some plastics are strongly corrosive against metals due to the generation of decomposition gases during the melting process. In this work the wear of Co-Cr-Mo alloy (hereafter CCM), Ni-based alloys, and steels in molten plastics was investigated using a newly developed wear tester. The specimens were rotated in molten glass fiber reinforced ethylene tetrafluoroethylene (ETFE) or polyphenylene sulfide

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... (PPS) at 10 MPa and 100 rpm for 50 h. CCM exhibited excellent wear resistance characteristics compared with the Ni-alloys and steels. The worn CCM surface was investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The formation of Cr and Co oxides was determined to play an important role in the resistance of CCM against corrosion. The thickness of the Cr and Co oxide layer reached to a depth of 160 nm from the top surface of the CCM specimen. CCM is thus a potential candidate for application to machine parts in polymer molding that are exposed to severe wear in decomposed gases.