| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系 === 99 === Three different tool steels of SKD61、SKD11 and SKH51 are coated with Nb at 950℃ in the borax bath containing niobium iron powders by thermoreactive deposition/diffusion. The impact tester was used to evaluate the effects of the niobium diffusion on coated SKD61、SKD11 and SKH51. The HRC and Hv hardness testers were used to observe the normal hardness and adhesion and cross-sectional hardness for the coated substrates and their films. The thermal gravity analysis (TGA) was used to investigate the thermal properties of the films when temperature up to 800℃. X-ray diffraction (XRD) and scanning electeon microscope (SEM) are applied to examine the phases and morphologies for the films and the boundaries between the substrate and the film. The results indicate that the impact energies are almost the same among the niobium coated tool steels. For the SKD11 deposition time of 5 hours、6 hours、10 hours, the thicknesses of the film deposition on SKD11 are 7.56μm、8.42μm and 8.86μm, respectively,while microhardnesses of Hv are 2413Hv25、2434Hv25、2420Hv25, respectively. For the SKH51 deposition time of 5 hours、6 hours and 10 hours, the thicknesses of the films deposition on SKH51 are 6.84μm、7.56μm and 7.56μm, respectively, while the microhardnesses are 2319Hv25、2323Hv25 and 2335Hv25, respectively. For the SKD61 deposition time of film of 5 hours、6 hours and 10 hours, the thicknesses of the films deposition on SKD61 are 4.54μm、5.62μm and 5.40μm, respectively, while the microhardnesses are 2096Hv25、2105Hv25 and 2081Hv25, respectibely. The XRD results show NbC phase grown on the surface of SKD61、SKD11 and SKH51, which in identified by elemental distribution analysis of SEM-EDS. The TGA results indicate NbC coated SKD61、SKD11 and SKH51 have superior abrasion resistance than uncoated those from the data of abrasion weight 0.0007~0.0009g for coated and 0.015~0.018g for uncoated SKD61、SKD11 and SKH51.
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