INFLUENCE OF THE NITRIDING AND TiAIN/TiN COATING THICKNESS IN THE MECHANICAL PROPERTIES OF A DUPLEX TREATED H13 STEEL

摘要

AISI H13 die steel substrates were low pressure gas nitrided in three different nitriding cases. In the nitriding case A, the surface hardness was around 12 GPa and the nitriding thickness was around 40 um. In the nitriding case B, the hardness was the same as in case A, but the nitriding thickness was around 70 urn. Finally, in the nitriding case C, the nitriding thickness was the same as in case B, but hardness profile showed a different behavior. In case C, the surface hardness was the same as case A and B. But the hardness increases as one move away from the surface showing the highest hardness at 15 um from the sample surface. The XRD results showed that the nitriding cases microstructure is composed mainly by the diffusion layer with small amount of Or_2N precipitates. These nitrided samples were subsequently coated with TiAIN using cathodic arc evaporation in two thicknesses of 3 and 7 μm. These samples were characterized with respect to phase chemistry, adhesion, hardness, elastic modulus and scratch tests. The phase chemistry determined through XRD revealed that coating was mostly Tio.7Alo.3N with some peaks of TiN which comes from the adhesion layer that was deposited prior to the deposition of TiAIN. The instrumented hardness performed in the coated samples showed that the coating system hardness changes with the nitriding cases when the coating thickness is 3 μm. On the other hand, the nitriding characteristics do not influence the coating hardness with thickness of 7 μm. In addition, the 7 μm thick coating is harder than the 3 μm thick coating. In the last part of this work, TiAIN was deposited in the AISI H13 substrate without nitriding; it was found that the hardness in this condition is higher than the nitrided/coated samples. The worn area, probed by the scratch test, was smaller for the TiAIN deposited over AISI H13 without the nitriding layer.