Superplastic forming (SPF) is an advanced manufacturing process, typically restricted to low volume and high value products, where metallic sheets are heated at the superplastic temperature and blow formed into a metallic die. Refractory ceramics are a low cost option to substitute the high temperature resistant steels and other alloys conventionally used in SPF dies, but their brittle nature is a limiting factor for most SPF applications. Suitable surface coatings have shown a significant effect on wear resistance in different applications and can be employed to improve the SPF ceramic performance in terms of tool life. This thesis addresses the lack of testing methods available to assess wear of dies under SPF conditions. A die-part interface (DPI) test method has been developed to assess wear of ceramic dies for sheet metal forming applications. In addition, the thesis discusses the employment of the DPI test to take strategic decisions in different material selection studies. A study is conducted on the comparison of two uncoated ceramic materials, Ceradyne ThermoSil ® 220 (ceramic CT) and Horizon Chrome infiltrated (ceramic HC), where DPI test results show that Ceradyne ceramic material has overall better performance under SPF conditions, thus its outcomes from the DPI test are considered the baseline to be compared with in further studies. Two deposition procedures of the same coating material, petalite, have been developed resulting in coating PET-A and PET-B. The resulting coatings are compared through DPI test, resulting in a better performance of the coating fired at higher temperature (PET-B). Three coating materials are assessed with the DPI test, which shows that two coatings soften under SPF conditions (F-50 and JK-N8), while another coating shows poor adhesion to the substrate (F-40). The thesis concludes presenting a DPI test protocol that proposes guidelines for die surface wear assessment under SPF conditions.
|Date of Award||17 Mar 2019|
- University Of Strathclyde
|Sponsors||University of Strathclyde & EPSRC (Engineering and Physical Sciences Research Council)|
|Supervisor||William Ion (Supervisor) & Lynne O'Hare (Supervisor)|