Effect of top and bottom filling on reliability of investment castings in Al, Fe, and Ni based alloys

The effect of bottom and top filling running systems on the properties of four investment cast alloys susceptible to contamination by oxide films during filling was studied. The alloys were air cast 2L99 Al-Si-Mg alloy and 254-SMO super duplex stainless steel and vacuum cast IN939 and IN738LC nickel based superalloys. The Weibull moduli for the tensile strength of investment cast bars produced using top and bottom filling were compared as indicators of casting reliability and of oxide damage produced by the running systems. A Weibull modulus of 18 was obtained for top filled 2L99 castings; this was increased to 34 when a correctly designed bottom filling system with a filter was used, thus reflecting the decreased scatter in properties. However, a similar effect was not found for the stainless steel. The use of improved running system designs led to minor increases in the Weibull modulus of the IN738LC and IN939 Ni alloys. MST/4609.