Manufacture and Analysis of Directional Solidification Organization of CMSX-6 Nickel-Base Superalloy

Xiangfeng Liang1,a, Yutao Zhao1,b, Zhenli Zuo1,c and Zhihong Jia1,d 1School of Material Science and Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, PR

China alxf20072833@163.com, bzhaoyt@ujs.edu.cn, c1017081843@qq.com, djia_zh@126.com

Keywords: High rate solidification; CMSX-6; Superalloys; Shrinkage porosity

Abstract. In this paper, we use the High rate solidification to study process parameters and

CMSX-6 super-alloy solidification structure. And then, it can provide more basis for the industrial

directionally solidified casting of superalloys blades. The results show that: under certain process

parameters, it can be obtained parallel columnar crystals directional solidification structure. The

organization is composed of the matrix γ phase and the secondary precipitated γ ' phase; under an

optical microscope, it can be observed the shrinkage porosity due to the volume’s reduction arising

solidification.

Introduction

As for the successful application of directional solidification, the most typical is reflected in

the super-alloys[1]. The super-alloys made by the directional solidification technology, were

basically eliminated transverse grain boundaries which are perpendicular to the stress axis,

wherewith its unique columnar grains or single crystal organization which are parallel to the

principal stress axis and preferred growth, what’s more, its superior mechanical properties, so,

super-alloys get long-term development[2-5]. Chen Chao[6] et who come from Shanghai Key

Laboratory of Modern Metallurgy and Materials Processing studied DZ417G alloy directional

solidification organizations, Jin tao[7] et who work in Institute of Metal Research Chinese Academy

of Sciences studied other coagulation parameters and microstructure of the nickel-base single

crystal superalloy DD98, but No one studied directional solidification structure of the nickel-base

superalloy CMSX-6 in China. Therefore, this paper mainly discusses nickel-base superalloy

CMSX-6 directional solidification structure, and makes foundation for the subsequent series of

experiment.

Experimental

The chemical composition of the master alloy ingot CMSX-6 superalloy is shown in table 1[8].

This test obtains directionally solidified structure by using vacuum induction directional

solidification furnace, and, the freezing method is HRS.

Table 1 The components of CMSX-6 alloy (wt %)

Alloy Co Al Cr Hf Mo Ti Ta Ni

CMSX-6 5.0 4.8 9.8 0.1 3.0 4.7 2.0 the

rest

The vacuum degree of this experiment is 0.015 Pa ~ 20 Pa, the cooling water keeps in 0.2MPa.

The mold shell was made by ourselves, the mold shell’s material is Al2O3, as shown in Figure1. In

the initial period, the induction furnace made CMSX-6 master alloy melting with continuously

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improving power. At the same time, the holding furnace would be heated to 1450℃ and 1500℃ by

the graphite heater according to the Fig.2 (which shows the temperature curve). And then we rise

the formwork which was put on the chillplate to the graphite heater. After heating the mold shell,

inject the molten metal CMSX-6 in it, and then maintain for 15 minutes after casting, so that it will

reach to thermally stable state. Then the mold shell removed from the heater at the speed of

3.5mm/min through the baffles.

Fig.1 The mold shell Fig.2 The temperature curve of the holding furnace

Results and discussion

When the induction furnace is completely cooled to room temperature, the shell mold is removed,

then we remove the surface material of the mold shell, and obtain the casting (Figure 3).

Fig.3 The casting

After sample preparation, sanding, polishing, metallographic etching. The composition of the

etching solution is 2g CuCl2, 2g NH4Cl, 5g FeCl3, 5ml HNO3, 50ml HCl and 80ml H2O[9], then,

using an optical microscope to observe the dendritic morphology (Figure 4(a), (b) ).

Key Engineering Materials Vols. 575-576 395

Fig. 4 (a) The Lowermost longitudinal and cross sectional microstructure

Fig. 4 (b) The longitudinal and cross – sectional microstructure which were 5cm away from the

lowest end of the casting

In the early period of the solidification, the way of heat loss mainly was the convective heat

which was based on the water-cooled, a certain distance after leaving the mold, it is mainly

converted to radiation cooling, so, the speed of the solidification is still faster[10, 11]. During the

experiment, when the directional solidification of the alloy reaches to steady state, the withdrawal

rate may be equal to the actual rate of solidification[12]. In the selected rate of movement of the

mold shell, the temperature gradient of the solid/liquid interface can also be approximately regarded

as not changed.

After specimens were polished and corroded using metallographic etchant, we used the optical

microscope to observe the dendrite and secondary precipitation phase morphology. In the Fig.4 (a)

and (b), we can see that dendrite between white light are the γ /γ ' eutectics. The cast

microstructures composed mainly by the matrix γ phase and secondary precipitation phase γ ', the

primary strengthening phase in nickel-based superalloys is γ '. Its size, shape and number had a

decisive influence on the ultimate mechanical properties of the alloy. Further, as shown in Figure 5

shrinkage porosity that exists in the CMSX-6 alloy directional solidification organization, the

volume decreases during solidification, it can lead to porosity.

Fig.5 Shrinkage porosity in the microstructure

396 Recent Highlights in Advanced Materials

However, during the directional solidification process, the upper part of the molten alloy

continually is replenished to the solidifying surface, so the porosity may be lower. But, it also may

appear shrinkage porosity in the dendrite roots, because the liquid may be insufficient to

supplement the volume difference made by the solid and liquid.

Conclusions

(1) In a certain process parameters, it can obtain directionally solidified structure for the

CMSX-6 super-alloy. The cross-sectional of the organization dendrite arms show regular cruciform

structure, and the longitudinal part are columnar crystals.

(2) CMSX-6 super-alloy by directional solidification process obtained casting structure

composed of matrix γ phase and secondary precipitated phase γ ' phase.

(3) The dendrite roots will appear shrinkage porosity during the solidification process.

Acknowledgements

This work was supported by Jiangsu (Industrial) Technology Support Project

(NO.BE2011142), Jiangsu Enterprise Academician Workstation Project (BM2009628).

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Recent Highlights in Advanced Materials 10.4028/www.scientific.net/KEM.575-576 Manufacture and Analysis of Directional Solidification Organization of CMSX-6 Nickel-Base

Superalloy 10.4028/www.scientific.net/KEM.575-576.394