Recent Advances in Cast Ni-Base Superalloys - Development/Modification/Applications

Since the late 1970’s and in response to gas turbine engine development requirements, Cannon-Muskegon Corporation has a legacy of developing commercially available, proprietary cast superalloys to meet industry needs. For single crystal cast superalloys, 2^ndgeneration, 3% rhenium-containing alloys such as CMSX-4®, PWA 1484 and Rene’ N5 have been used extensively in the hot section of both aero and industrial gas turbine engines.  However, competing criteria of oxidation and high temperature capability, cost and producibility have provided the impetus for more recent SX alloy developments which are impacting materials selection for new and improved engine applications.

Development of lower sulfur technology has produced an improved CMSX-4® alloy with superior oxidation and coating performance particularly for unshrouded high pressure turbine blade applications, which are often thermal barrier (TBC) coated. 

CMSX-4® Plus [4.8% Re] is an improved 3^rd generation SX alloy which demonstrates major advances in high temperature strength properties over 2^nd generation CMSX-4 alloy, excellent castability, improved heat treatment window, phase stability (SRZ/TCP), and lower Re content, cost and density compared to 3^rdgeneration CMSX-10K® alloy [6.3% Re].

CMSX®-8 alloy is a new SX alloy with creep-rupture properties similar to CMSX-4 alloy to 1900°F (1038°C), but with half the Re content (1.5%) making this a cost-effective alternative to 2^ndgeneration SX alloys for applications with less demanding high temperature casting requirements.  CMSX®-8 [B/C] alloy provides improved accommodation for grain defects such as low angle boundaries in difficult to cast SX multi-vane segments and large IGT turbine components.

In the area of conventionally cast superalloys, CM 939 Weldable® is a chemistry modified, proprietary version of IN 939 with improved ductility and phase stability which is structurally weld repairable.

Each of these alloy developments will be discussed including the design motivation, alloy characterization (heat treatment, mechanical and physical properties), castability and applications.