Low-temperature plasma nitriding of titanium layer on Ti/Al clad sheet

A nanostructured surface layer was fabricated on titanium layer of a Ti/Al clad sheet composite by means of the surface mechanical attrition treatment (SMAT). The low-temperature plasma nitriding treatment of the SMAT sample was investigated in comparison with the coarse-grained sample by using structural analysis (X-ray diffraction, scanning electron microscopy, and transmission electron microscopy) as well as mechanical and corrosion property measurements. Results showed that the nitriding kinetics of the SMAT sample with the nanostructured surface layer was greatly enhanced, so that the nitriding temperature could be as low as 550 °C, which is significantly lower than the melting point of the aluminum layer on Ti/Al clad sheet (conventional nitriding can lead to melting of the aluminum layer due to higher temperature about 800 °C). The nitrided layer of the SMAT sample was composed of nanostructured ε-TiN and γ-Ti2N phase with high supersaturation of nitrogen. The surface hardness and the hardened surface layer thickness as well as the wear and corrosion resistances of the nitrided SMAT sample were all substantially enhanced relative to the nitrided coarse-grained sample.

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► A nanostructured surface layer was produced on titanium layer of Ti/Al clad sheet.
► The SMAT process is able to enhance nitriding kinetics at low temperature (550 °C).
► The aluminum layer on Ti/Al clad sheet had not been destroyed during nitriding.
► The hardness value of the nitrided SMAT sample is about 1288 HV at the top surface layer.
► The wear and corrosion resistances of the nitrided SMAT sample enhanced obviously.