摘要:

AbstractIn high temperature alloys, the selective oxidation of chromium to form a chromia scale leads to subsurface depletion of chromium in the alloy which in turn leads to the dissolution of chromium carbide in the depleted zone. The effect of this carbide depleted subsurface zone on the creep properties of Inconel Alloy 617 (Ni–22Cr–12Co–9Mo–1Al–0·08C; wt-%) has been determined. The specimens were subjected to heat treatments before creep testing to simulate long term service exposure of a thin walled heat exchanger tube operating at high temperatures. It was found, surprisingly, that in creep tests carried out at 900°C, specimens having extensive chromium depleted and carbide free subsurface zones exhibit higher creep strength than specimens thermally aged for the same durations, but having no chromium depleted zone. As chromium was removed from the matrix owing to selective oxidation, the carbon, released as the carbides in the chromium depleted zone dissolved, migrated to the centre of the specimen, producing enhanced carbide precipitation. This led to an increase in the creep strength of the specimen core, which offset the loss in creep strength of the subsurface zone. The expected detrimental effect of chromium depletion was therefore not observed.MST/1487

ISSN:0267-0836    

DOI:10.1179/026708392790169812

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractResults are reported concerning the effect of thermal treatments in the temperature range 1050–1500°C for 1–1000 h on the stability of the t′phase present in laser sealed layers of ZrO2–8·5 wt-% Y2O3. Aging for up to 1000 h at 1050°C is not sufficient to cause significant transformation of the t′phase. At temperatures>1300°C, the t′phase is less stable and transforms to mixtures of the t and c phases in proportions which are a function of both the time and temperature of aging. An improvement in the fracture toughness of the sealed layer was found to occur when substantial proportions of t phase were produced by annealing.MST/1529

ISSN:0267-0836    

DOI:10.1179/026708392790169867

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/026708392790169849

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor