Graduate Thesis Or Dissertation
 

Thermal stability of surface treated zirconium

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xw42nb47n

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  • Zirconium press plates have been developed for the production of melamine coated particle board, using shot-peening to achieve the desired plate (and therefore coated particle board) surface texture. Service temperatures of the press plates approach 200°C. This study examined the microstructural effects of extended exposure of shot-peened zirconium to temperatures of 200°C and 300°C. Softening of the surface may reduce wear resistance and possibly the surface morphology of the plate, affecting the usability of the plates. It was discovered that the shot-peened surface of the plates experienced a loss in hardness from approximately 230 VHN (DPH) to about 220 VHN after 560 hrs at 200°C. The same drop in hardness was experienced after only 5.5 hrs at 300°C. This decrease in hardness was determined from hardness profiles before and after heat treating the zirconium to various times from 0.5 hours to 4458 hrs and 2790 hrs at 200°C and 300°C respectively. The decrease in hardness is believed to be a result of static recovery, the annihilation of point and/or line defects and/or alignment of dislocations into relatively low misorientation substantially relatively close to the shot-peened surface (about 35 μm), and decreased more modestly over the next 100 μm until virtually no drop was experienced further than approximately 150 μm from the surface. The shot-peening hardens the surface region which extends about 150 μm from the surface. Thus, the level of recovery appears to depend on the stored energy associated with cold work, or ambient temperature deformation. This increases from about 2-3% cold work (equivalent percent cold reduction from rolling) in the bulk of the specimens to near 99% at the surface resulting from shot-peening. The dislocation structure of the shot-peened zirconium was examined in the as-peened as well as the annealed conditions using transmission electron microscopy.
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