An investigation on the creep and fracture behavior of cast nickel-base superalloy IN738LC
- PDF / 2,374,413 Bytes
- 7 Pages / 603.28 x 788 pts Page_size
- 22 Downloads / 330 Views
I.
INTRODUCTION
C A S T nickel-base superalloys have been successfully used in gas turbines for blades and vanes exposed to long periods of service at high temperatures. Thus their creep resistant properties are very important for engineering design. These properties depend on such factors as solid solution hardening of the fcc 31matrix, grain boundary strengthening by carbides, and most important, on the ability of precipitates of the ordered 3" phase to impede dislocation motion, t However, the past investigations2'3,4 focused mainly on the minimum creep rate and stress rupture properties, whereas the three-stage creep behavior of cast superalloys had received little attention. 5'6 The purpose of this investigation is to explore in further detail creep-rupture behavior, the creep deformation processes, and the factors controlling the tertiary creep and fracture behavior of the IN 738LC alloy.
II.
EXPERIMENTAL PROCEDURE
IN738LC is a multiphase alloy consisting of 3, matrix, 7', M3B2, and TiN. The nominal composition of the 3/phase is Ni3(A1, Ti) with some substitutional elements present. The volume fraction of 3" phase is - 4 8 pct. In this alloy the 3" phase exists in three forms: the degenerate 3-3" eutectic having a mushroom-like arrangement of 3" particles with the 3' in ribbons; the primary 3" particles having cubic form which frequently assumes a more degenerate shape after heat treatment, but that will be considered as cuboids, and their edges are about 0.43/xm; the fine 3" particles precipitated during aging with a size of approximately 0.11 /~m which presents a spherical shape (Figure 1). The creep tests were conducted at 750 to 950 ~ and at various constant loads on a Denison Model T48 testing machine. The temperature was measured with two thermocouples placed at each end. The stability of the furnace temperature during creep tests was about ___1 ~ An inductive transducer could detect strain variations as small as 2 x 10-6. The output from the transducers was automatically measured and printed out at any required time interval. M23C6, M E ,
The material used in this investigation has been supplied by Henry Wiggin in the form of 76 mm diameter cast bars. This material was then recast by Howmet Company under the form of overdimensioned specimens and lastly machined to size after heat treatment. Table I gives the composition of the material after casting. Required porosity level was from 5 to 7 pores mm -2 with maximum pore size of 0.1 to 0.12 mm. The grain size was found to be approximately 2 mm as determined by linear intercept. The heat treatments consisted of two hours at 1120 ~ in vacuum followed by cooling to room temperature at a rate equivalent to air cooling, then 24 hours at 845 ~ in argon followed by cooling to room temperature at a rate equivalent to air cooling. GUO JIANTING is a Visiting Professor at the Institute of Technology for Non-Traditional Metals (I.T.M.) -C.N.R., on leave from Institute of Metal Research Academia Sinica, Wenhua Road, Shenyang, China. D. RANUCCI and E. PICCO are
Data Loading...
