Turbine Blade Alloy Research Articles

Forging of blades for gas turbines

AbstractForging technology has been developed to the point where wrought nickel alloy turbine blades can be manufactured to accurate dimensional tolerances and consistent metallurgical characteristics. Metallurgists and engineers have utilized theoretical knowledge and practical understanding of nickel superalloys and the forging process to meet the ever-increasing temperature and stress demands of turbine engines. New materials, forging techniques, and the use of computer-aided design and manufacturing systems are being developed to compete with advanced casting technology.MST/259

Effect of chloride concentration and pH on fatigue crack initiation morphology of Type 403 stainless steel

Corrosion fatigue studies have been conducted on martensitic Type 403 turbine blade alloy in air, deaerated distilled water, and deaerated 0·01 and 1M NaCl solutions at pH 2, 7, and 10 at 100°C. At the same value of applied stress, the fatigue life in distilled water was almost the same as that obtained in air, while in chloride solutions the fatigue life was drastically reduced. The difference in fatigue life was attributed to the influence of chloride induced corrosion pits on crack initiation and to the effects on crack propagation of the change in solution chemistry at the tips of growing fatigue cracks. In 1M chloride solution at pH 10, the application of cyclic stressing promoted the development of corrosion pits, which did not form in unstressed material. A morphological investigation of crack initiation has shown that branched cracks and debonded regions developed at non-metallic inclusions in specimens fatigued in air. In contrast, cracks initiated in a transgranular mode in distilled water. Cracks initiated from corrosion pits were observed in all chloride solutions, except 0·01 M chloride solution at pH 10 where cracks initiated by an intrusion-extrusion mechanism.

Evaluation of High-Temperature Alloys for Helium Gas Turbines

Because of the high thermal and mechanical stresses in components of a helium turbine coupled directly to a high-temperature reactor and the stringent nuclear safety requirements, an extensive materials development program has been undertaken. The candidate alloys for turbine blades and hot ducts (nickel- and molybdenum-base alloys) and for rotors (1% CrMoV and 12% chromium steels) have been tested under the expected service conditions.The results of creep/rupture, fatigue, and fracture mechanics tests on turbine blade and rotor materials are presented. The gas/metal reactions that occur in the simulated reactor coolant gas and the decontamination behavior of components are also discussed. In addition the development of a molybdenum-base alloy for turbine blading is reported.

Improvement of Creep strength in a nickel-base single-crystal superalloy by heat treatment

The effect of two heat treatments on the creep behaviour of CMSX-2, a recently developed nickel-base single-crystal turbine blade alloy, was investigated in the temperature range 760–1050 °C. It is shown that the heat treatments had no effect on the γ′ volume fraction, the composition of precipitates and the coherency strains. However, the heat treatment resulting in cuboidal aligned precipitates, 0.45 μm in size, leads to a two-fold improvement in creep lives over the corresponding values obtained with the other heat treatment which produces smaller and more odd-shaped particles. Transmission electron microscopy on specimens crept to various strains at 760 °C showed that, in contrast with the odd-shaped particles, the cuboidal precipitates promoted a very homogeneous deformation which led to the lower creep rates. The precipitate shearing mechanism in the late stages of primary creep is shown to be by {111}〈112〉 slip regardless of the heat treatment. In secondary creep the shearing occurs by (α/2)〈110〉 dislocation pairs but the difference in creep behaviour is thought to be associated with the higher stability of dislocation networks associated with cuboidal precipitates. At 1050 °C the more perfect rafted structure produced by the cuboidal precipitates is responsible for lower creep rates. The γ′ rafts at high stresses were sheared by (α/2)〈110〉 dislocation pairs.

Damping in Turbine Blade Alloys

Abstract Measurements of the damping capacity Q−1 of candidate turbine blade alloys for the Wairakei, New Zealand geothermal power station and other future power stations are reported. The techniques used were the piezoelectric ultrasonic composite oscillator technique (PUCOT) at 40 or 80 kHz and stress levels 70 kPa to 37 MPa and the vibrating reed technique (VRT) at 321 Hz and stress levels 32 to 177 MPa. Specimen materials investigated were Ti-6A1-4V, 26Cr-1Mo steel, Firth-Vickers (United Kingdom) FV520B steel, 15Cr-Mo steel, and 410 (Unified Numbering System [UNS] S41000) stainless steel. The results include Young's modulus and the stress and strain amplitude dependences of Q−1. The frequency dependence of Q−1 was found to be only a few tens of percent, much smaller than the predicted dependence. Of the two techniques, it was shown that the VRT is more suited to damping measurements at the operational stress levels for turbine blades. The PUCOT, VRT, and high stress cyclic stress-strain data were plotted on a universal curve of damping energy versus stress. The plot covers 14 orders of magnitude in damping energy and five orders in stress.

Dod Applications of Implantation-Modified Materials

ABSTRACTThis paper reviews areas under investigation within DoD involving the application of ion implantation to problems in wear, friction, corrosion, and fatigue. Specific results on the modification of metal fatigue in Ti turbine blade alloys and the modification of sliding wear of steels are reviewed and discussed in terms of the mechanisms which are thought to be acting to improve the metal properties.

Determination of the elastic moduli of a directionally solidified nickel-based TaC eutectic

Measurements of ultrasonic wave velocities in a polycrystalline directionally solidified nickel based eutectic alloy are used to evaluate the three independent single crystal elastic moduli at temperatures between 298 to 925 K. The Cu and C44 moduli are obtained directly from high frequency wave propagation along the D.S. axis, corresponding to . Evaluation of C12 requires measurements at lower frequencies to obtain (C11 −E ). The elastic anisotropy and temperature dependence of the elastic moduli are almost identical to those reported for pure Ni, indicating that neither TaC fiber reinforcement nor γ′ precipitate have strong effects on elastic properties of Ni based turbine blade alloys.

Effects of Chromium, Molybdenum, and Tungsten on Sodium Sulfate-induced High Temperature Corrosion of Nickel

Abstract Operating gas turbine engines are susceptible to a phenomenon called hot corrosion. Hot corrosion is generally attributed to the interaction of nickel-base turbine blade alloys with ingested sodium sulfate. Two mechanisms were presented previously to account for the surface and grain boundary corrosion of nickel metal. This paper reports the effect of chromium, molybdenum, or tungsten, or their corrosion products on the corrosion of nickel metal. The corrosion products considered are the oxides and sodium-oxygen compounds. The corrosion products of molybdenum and tungsten enhance the sodium sulfate-induced corrosion of nickel to the same degree as the metals themselves while those of chromium do not. The enhanced corrosion caused by sodium molybdate or tungstate suggests that more than a simple acid-base phenomenon is involved. The formation of a friable, porous film caused by the presence of nickel molybdate or tungstate is proposed as the mechanism responsible for this enhancement. This mechani...

Fatigue crack growth in a cast Ni-base alloy

The potential drop technique has been used to measure fatigue crack propagation rates in the cast nickel base turbine blade alloy, IN 738 LC. The dependence of the growth rate on the cyclic stress intensity amplitude has been determined at different values of the applied static load and at temperatures up to 850°C. Optical and scanning electron micrographs have revealed significant differences in the mode of fracture.

The Use of Proton-Excited X-Ray Emission to Study: 1) Electrodeposited TiB2 Coatings and 2) Gas-Turbine Blade Failures

A method to quantitatively analyze the surface regions of metals, alloys, and coatings using proton-excited X-ray emission (PEX) has been utilized in two areas of metallurgy research. This paper describes application of the technique to (1) the development of erosion- and corrosion-resistant coatings, and (2) the study of structural failures in turbine alloys.The technology for the electrodeposition of erosion- and corrosionresistant TiB2 coatings from molten-salt electrolytes has been developed in order to provide protective coatings for valve components in coal gasification plants. Analyses by PEX and X-ray diffraction have played the key role in the determination of the optimum electrolysis parameters required to obtain adherent, erosion-resistant TiB2 coatings. From these studies, the erosion resistance of a TiB2 coating can be predicted on the basis of (1) the amount of Cr and Fe impurities codeposited during electrolysis and (2) the degree of orientation of the TiB2 crystal structure along the (110) or (100) planes.PEX was used for analytical studies of a Nimonic 105 alloy turbine blade and an A-286 alloy turbine wheel from a San Diego, California, power generating station gas turbine that suffered a catastrophic failure in November 1974. Analyses of the turbine blade in the region at which the rupture occurred showed alloy composition changes that included decreases of 80%, 78%, 52%, and 50% of Al, Ti, Cr, and Co, respectively, and an increase of 2500% in Fe. Alloy composition changes were also found at the failure interface of the turbine wheel; these included decreases of 43%, 21%, and 15% in Hi, Cr, and Ti, respectively, and increases of 248% and 714% in Si and Al, respectively.

Strength of turbine-blade alloys in supersonic gas flows

Strength of turbine-blade alloys in supersonic gas flows

Ultrafine dispersion-strengthening of tungsten by chemical covapor deposition

A method of dispersion-strengthening tungsten, a refractory metal, with submicron (< 10 Å) dispersoids of hafnium nitride, a stable ceramic, is described. Simultaneous deposition of the metal and the dispersoid is achieved by a chemical vapor deposition process called covapor deposition. The tungsten and hafnium are covapor deposited by hydrogen reduction of their halides (WCl 6 and HfCl 4); the dispersoid is formed during deposition by the reaction of hafnium with NH 3 in the hydrogen gas. The microstructure of the tungsten matrix, either the large columnar grains typical of chemical vapor deposited tungsten or fine noncolumnar grains (< 1 μm), can be controlled by varying the deposition parameters. It is also possible by varying these parameters to change the number, size, and spacing of the dispersoids. The deposits were heat treated at 1700 °C for at least 1 h before hot microhardness values to 1400 °C were determined. These values were then compared with hot microhardness values determined after heat treatment for 96 and 500 h at 1700 °C. The microstructures of the deposits in these conditions were evaluated by thin film and scanning electron microscope techniques. The hot microhardness of the LRL dispersion-strengthened tungsten was superior to that of dispersion-strengthened tungstens prepared by other techniques. The possibilities of using this technique to improve the strength and creep resistance of other metals ( e.g., nickel-chromium alloys for turbine blades) is also suggested. Parameters are given for the deposition of pure tungsten and hafnium nitride from their halides.

An Investigation of Heat Flow in Unidirectional Solidification of Vacuum-Cast Airfoils

In order to better understand the thermal events occurring during the unidirectional solidification of Mar M-200 (proprietary alloy of Martin-Marietta, Inc.) alloy turbine blades, an analytical thermal model was developed which permitted simulation of the solidification process. A representative turbine blade was divided into isothermal nodes, and an electrical analog thermal model was constructed and solved using a digital computer. The technique was verified by comparing calculated and measured external mold surface temperatures during solidification. The analytical thermal model showed that thermal gradients in the liquid–solid growth zone are high near the chill, and decrease as the distance from the chill increases. Temperature profiles were converted into solidification profiles from experimental data which showed the percent solid as a function of temperature in the solidification zone. The curves permit a qualitative explanation of the occasional occurrence of segregation and hot cracking in this alloy, and indicate that precautions must be taken in the solidification process to avoid these phenomena.

Investigation into the fatigue life of turbine blade alloys and structural elements under thermal cycling conditions

Investigation into the fatigue life of turbine blade alloys and structural elements under thermal cycling conditions

The development and testing of protective coatings on F48 and SU16 niobium alloys

N.G.T.E. interest lies in the development of coatings that will protect niobium alloy turbine blades up to 1300 °C. A silicide-glaze composite coating has been developed which protects F48 and SU16 niobium alloy during laboratory oxidation tests at temperature up to 1300 °C and has useful creep resistance at temperatures up to 1250 °C. The oxidation resistance of the N.G.T.E. coating compared favourably with a Cr-Ti-Si coating developed commercially in the U.S.A., and was found to be superior to several other experimental coatings.