Manufacture of an article by hot isostatic pressing

Abstract

In a hot isostatic pressing (HIP) process, for example for securing blades ( 5 ) to a disc ( 3 ) to form a blisk ( 1 ), the temperature of the powder ( 6 ) to be consolidated is raised to a predetermined temperature, which may be the eventual required pressing temperature, before the pressure rise to the pressing pressure is initiated. If the powder is a titanium alloy and the process employs steel tooling pieces, the application of pressure occurs only when the temperature has risen to the extent that the steel is harder than the titanium alloy.

1 . A method of manufacturing an article by hot isostatic pressing of a powder using a tooling piece, wherein the powder comprises a first material and the tooling piece comprises a second material, the powder material being harder at ambient temperature than the tooling piece material, the method comprising:
 raising the temperature of the powder to a pressing temperature; and,   applying a pressing pressure to the powder by the tooling piece,   characterised in that the relative hardness of the first and second materials varies with temperature and   the pressure applied to the powder is maintained below the yield stress of the second material until the temperature of the powder is greater than a predetermined temperature at which the hardness of the two materials is equal.   
     
     
         2 . A method as claimed in  claim 1 , wherein the pressing temperature is greater than the predetermined temperature such that the first material is softer than the second temperature upon pressing. 
     
     
         3 . A method as claimed in  claim 1 , wherein the powder comprises a metallic material. 
     
     
         4 . A method as claimed in  claim 3 , wherein the powder comprises a titanium alloy. 
     
     
         5 . A method as claimed in  claim 1 , wherein the tooling piece comprises a metallic material. 
     
     
         6 . A method as claimed in  claim 5 , wherein the tooling piece comprises steel. 
     
     
         7 . A method as claimed in  claim 5 , wherein the tooling piece comprises a steel body provided with a ceramic coating. 
     
     
         8 . A method as claimed in  claim 1 , wherein the predetermined temperature is greater than 400° C. 
     
     
         9 . A method as claimed in  claim 8 , wherein the predetermined temperature is not less than 100° C. lower than the pressing temperature. 
     
     
         10 . A method as claimed in  claim 9 , wherein the predetermined temperature is approximately equal to the pressing temperature. 
     
     
         11 . A method as claimed in  claim 1 , wherein the temperature of the powder is raised from ambient temperature to the pressing temperature over a first time period, the applied pressure is raised from a holding pressure to the pressing pressure over a second time period which begins when the temperature has reached the predetermined temperature, and the pressing temperature and pressing pressure are maintained for a third time period from the end of the second time period. 
     
     
         12 . A method as claimed in  claim 11 , wherein the first time period is not less than 2.5 and not more than 3.5 hours. 
     
     
         13 . A method as claimed in  claim 11 , wherein the second time period is not less than 1.5 hours and not more than 2.5 hours. 
     
     
         14 . A method as claimed in  claim 11 , wherein the third time period is not less than 2.5 hours and not more than 3.5 hours. 
     
     
         15 . A method as claimed in  claim 1 , wherein the article is a bladed disc for a gas turbine engine.