Microstructural Parameters Controlling High-Temperature Creep Life of the Nickel-Base Single-Crystal Superalloy MC2
- PDF / 1,241,213 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 28 Downloads / 204 Views
N
MONOCRYSTALLINE nickel-base superalloys are widely used in the hottest parts of aircraft turboengines.[1] Blades made of these alloys operate for thousands of hours at temperatures as high as 1373 K (1100 C).[2] These alloys are chosen for their superior mechanical performances at high temperatures, in particular their high-temperature creep resistance for uncooled components such as high-pressure turbine blades of turboshaft engines in helicopters or small industrial gas turbines. These interesting properties result from the precipitation of a high volume fraction (close to 70 pct) of the long-range ordered L12 c¢ phase, which appears as cubes coherently embedded in a facecentered cubic (fcc) solid solution c matrix. JEAN-BRIAC LE GRAVEREND, Ph.D. Student, is with the Office National d’Etudes et de Recherches Ae´rospatiales (ONERA), BP 72, 92322 Chaˆtillon, France, and with the De´partement Physique et Me´canique des Mate´riaux, Institut P’, UPR CNRS 3346, CNRSENSMA-Universite´ de Poitiers, F86961 Futuroscope Chasseneuil Cedex, France. Contact e-mail: [email protected] JONATHAN CORMIER, Associate Professor, and JOSE´ MENDEZ, Professor, are with the De´partement Physique et Me´canique des Mate´riaux, Institut P’, UPR CNRS 3346, CNRS-ENSMA-Universite´ de Poitiers. SERGE KRUCH, Research Engineer, is with the Office National d’Etudes et de Recherches Ae´rospatiales (ONERA) and also, Associate Professor, with the Mines Paris Tech, 75006 Paris, France. FRANCK GALLERNEAU, Research Engineer, is with the Office National d’Etudes et de Recherches Ae´rospatiales (ONERA) and also, Deputy Director, with the De´partement Mate´riaux et Structures Me´talliques, Office National d’Etudes et de Recherches Ae´rospatiales (ONERA). Manuscript submitted August 26, 2011. Article published online May 30, 2012 3988—VOLUME 43A, NOVEMBER 2012
High-temperature creep properties of these alloys are often improved by increasing the amount of refractory elements (e.g., W, Mo, Re, etc.),[3] although this often leads to topologically close-packed (TCP)-phase formation (r, l, P, and R phases as it can be observed in second-, third-, and fourth-generation alloys).[4–8] TCP phases are known to form first in dendrite core regions in single-crystal superalloys[9,10] because of the residual microsegregation of Re, W, Mo, and Co across the dendritic structure, which can only be partially removed using standard solutionizing treatments.[11–13] In the case of the MC2 alloy, which is free of rhenium and ruthenium, the preferential TCP phase formed during high-temperature (1223 K [950 C] < T < 1423 K [1150 C]) exposure is the l-type phase (rhombohedral crystal, 4.75 £ a £ 4.80 A˚ and a = 31 deg), rich in W, Mo, Co, and Cr.[14] The l-phase precipitates along h110i orientations on {111} planes and exhibits three kinds of morphologies (needle, platelet, or globular shape). The l-phase precipitates semi-coherently with the matrix, which may explain its strong influence on the surrounding microstructure. Moreover, l-phase is known to have detrimental effe
Data Loading...
