Hot cracking in the HAZ of laser-drilled turbine blades made from René 80

Abstract

Advanced film cooling technologies for hot gas path components in gas turbine engines with still constantly increasing inlet temperatures require special manufacturing processes. Today, laser radiation is the preferred means of drilling a large number of small-diameter cooling holes in turbine parts made of nickel-base superalloys. Most of these materials, however, exhibit a relatively high susceptibility to hot cracking in the heat affected zone (HAZ) adjacent to the recast layer. Comprehensive metallographical examinations have been performed to optimise laser drilling parameter settings to minimize hot cracks. In the case of René 80, there seems to be a pronounced microstructural influence on hot cracking sensitivity, i.e. identical laser parameters may produce quite different crack lengths, dependent upon local microstructure in the immediate vicinity of the drilled hole. Grain size, grain boundary morphology and orientation, and primary carbide distribution apparently have a significant influence. These interdependencies should be taken into account when acceptable crack lengths are specified. As far as conventionally investment cast components are concerned, influencing local microstructural features with economically viable effort may be unrealistic.

Probabilistic Modeling of Slip System-Based Shear Stresses and Fatigue Behavior of Coarse-Grained Ni-Base Superalloy Considering Local Grain Anisotropy and Grain Orientation

“…Cylindrical bars with 150 mm length made of the polycrystalline Ni-base superalloy René80 [35][36][37][38][39], were conventionally casted and heat treated by Doncasters/Germany. To achieve the final microstructure, a two-step heat treatment consisting of solution annealing and aging was applied to the material.…”

Laser Treatment of Rene-41: Thermal and Microstructural Analysis

“…Consequently, investigation into laser surface treatment of Rene 41 and thermal stress development in the treated layer becomes essential. Considerable research studies were carried out to examine laser processing of superalloys [2][3][4][5][6][7][8]. However, the previous studies were focused on the microstructural analysis and thermal stress fields were left obscure.…”

Microstructural Response of Directionally Solidified René 80 Superalloy to Gas-Tungsten Arc Welding

“…It is designed to withstand service temperatures of up to 980°C. [1] The alloy possesses a very good hot-corrosion resistance, long-term stability, and high-temperature strength, primarily due to the precipitation hardening by c¢ precipitates, an ordered intermetallic Ni 3 (Al,Ti) phase dispersed in the austenitic (c) matrix. Directional solidification processing of the alloy results in a further improvement in its high-temperature properties and hotcorrosion resistance and also permits the use of higher service temperatures, which is very important for enhancing the thermal efficiency of turbines.…”

“…[13][14][15] Residual welding stresses and aging-contraction stresses, combined with a low ductility of the alloy due to localized melting along the HAZ grain boundaries during welding, are the major factors responsible for the PWHT cracking. [6][7][8][13][14][15] Therefore, there is a need to study the microstructure of the welded superalloys in order to (1) understand the formation of defects in the welds and (2) be able to develop appropriate postweld heat treatment(s) for relaxation of residual welding stresses and microstructural homogenisation. However, because no detailed information is available on the microstructure of welded DS Rene´80 alloy, the present investigation was undertaken to study the microstructural response of DS Rene´80 alloy to gas-tungsten-arc (GTA) welding.…”

“…pct) exhibit only a limited weldability due to their low crack resistance to heat-affected zone (HAZ) cracking during welding and during the subsequent postweld heat treatment (PWHT). [6][7][8][9][10][11][12][13][14][15] Heat-affected zone cracking, observed in many precipitation-strengthened alloys during welding, is generally attributed to (1) shrinkage stresses caused by rapid reprecipitation of c¢ particles during weld cooling and (2) the propensity of the alloys to liquation cracking due to constitutional liquation of various phases normally present in the preweld microstructure of the base alloy. [6][7][8][9][10][11][12][13][14][15] Strain-age or PWHT cracking, which affects all the precipitation-hardened superalloys, has also been reported to generally initiate in the HAZ that liquated during the welding process.…”