2001, Volume 3, Issue 5
Strategic Study of CAE >> 2001, Volume 3, Issue 5
The Near β Forging Overthrows the Conventional Forging Theory and Develops a New Tri-modal Microstructure
Northwestern Polytechnical University, Xi'an 710072, China
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Abstract
The near beta forging for titanium alloys proposed by the authors has overthrown the conventional forging theory in the following two aspects: firstly, the material is heated and forged at 10〜15℃ below beta transus temperature and then water cooled; secondly, the heat treatment technology after forging consists of a high-temperature toughening treatment and a low-temperature strengthening treatment instead of the conventional aging treatment. Because of ingenious combination of phase transformation, defomation and strengthening and toughening theory, materials forged by the near beta forging do not produce an equiaxed microstructure or a basketweave microstructure as usually found in conventionally forged titanium alloy, but do produce a new trimodal microstructure, which consists of about 20% equiaxed alpha, 50%～60% basketweave formed by striature alpha and transformed beta matrix. The trimodal microstructure not only develops a new type of microstructure in addition to the existing four titanium alloy microstructures (i.e. equiaxed, bi-modal, basketweave and lamella), but also has the advantages that both the equiaxed microstructure and the basketweave microstructure have, so it shows excellent mechanical properties. It shows an increased high-temperature property, a high low-cycle fatigue property and a high fracture toughness without decreasing ductility and thermal stability. Moreover, it can raise the service temperature from 500℃ to 550℃ . The near beta forging is applicable not only to alpha-beta alloy, but also to alpha, near alpha and near beta titanium alloys. This method has been used to forge several engine compressor disks and some important structure components of missils and airplanes
Keywords
titanium alloy ; near beta forging ; tri-modal microstructure
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