Hardness, microstructure and surface characterization of laser gas nitrided commercially pure titanium using high power CO{sub}2 laser

摘要

Surface nitriding of commercially pure (CP) titanium was carried out using high power CO{sub}2laser at pure nitrogen and dilute nitrogen (N{sub}2 + Ar) environment. The hardness, microstructure,and melt pool configuration of the laser melted titanium in helium and argon atmosphere wascompared with laser melting at pure and dilute nitrogen environment. The hardness of the nitridedlayer was of the order of 1000 to 1600 HV. The hardness of the laser melted titanium in the argon andhelium atmosphere was 500 to 1000 HV. Using x-ray analysis the formation of TiN and Ti{sub}2Nphase was identified in the laser nitrided titanium. The presence of nitrogen in the nitrided zone wasconfirmed using secondary ion mass spectroscopy (SIMS) analysis. The microstructures revealeddensely populated dendrites in the sample nitrided at 100% N{sub}2 environment and thinlypopulated dendrites in dilute environment. The crack intensity was large in the nitrided sample at purenitrogen, and few cracks were observed in the 50 % N{sub}2 + 50 % Ar environment.