Isothermal rolling is performed with refractory metal rolls and uses electrical resistance to heat a local region of the roll and the workpiece for shaping. Reductions of 90 percent per pass can be achieved by this process using forced feed of the workpiece into the rolls. Ring rolling is performed with a small modification of the equipment, and many of the processes used to roll straight sections have been applied to rings. Isothermal ring rolling starts with readily available barstock that is cold rolled to a circular blank and fusion welded. Isothermal rolling works the weld and produces a net shape of high quality. Very significant savings result from reduced metal consumption and elimination of major machining costs. Two methods of gage control and two methods of diametrical control are discussed. Circumferential control within 0.01 percent has been demonstrated, although subsequent stress relief and sizing by cold expanding are recommended in most cases. Examples of ring rolling in steel, titanium, and superalloys are described.

Ultrasonic imaging is taking a larger and larger role in the NDE of turbine engine materials and in support of fracture mechanics calculations. It is also playing an increasing role in quality and process control. For most fracture toughness calculations, it is necessary to establish the accuracy with which a flaw’s size and shape are imaged, whether single or multiple flaws are involved, and the spacing of multiple flaws. Because of these requirements, resolution has become an issue as well as detection sensitivity. There are a number of resolution targets that can provide this type of calibration information for an ultrasonic imaging system. A fused quartz USAF 1951 target, similar to the patterns used in this work, was first used by Gilmore (1986), but Gilmore’s pattern was superficial and subsurface evaluations were limited to focusing on the pattern from the opposite side of the blank and monitoring the reflection from what is now the target backwall. Work by Peyton (1977) did produce buried targets in titanium samples, but there was no practical method to produce buried targets in high-temperature ceramics until the techniques developed by Rodel and Glaeser (1987) were used to produce the targets described in this paper. Optically transparent resolution targets make it feasible to visually verify that the resolution target has been correctly fabricated. An image of the target with a candidate ultrasonic transducer then permits quantitative image resolution estimates to be made even when the interrogating acoustic beam contains significant refractive aberration. This is important because useful subsurface images can be acquired with the use of acoustic beams that are aberrated to the point that diffraction-limited beamwidth calculations are meaningless. This work also demonstrates how the interdisciplinary skills of manufacturing companies can be combined with those of universities to produce results that any one of the individual members of the team could not have produced alone, without significant increases in labor, time, and cost.

Degradation of microstructure and mechanical properties of a service run GTD-111 DS blade was evaluated. The blade was coated with a CoCrAlY coating (GT-29) and had operated on a GE Model MS 5002 engine for 54,850 hours. To recover the microstructure of the degraded blade, the effect of solution treatment temperature on the microstructure and properties was evaluated. The blanks removed from the airfoil tip section were given a commonly used partial solution treatment 2050°F (1120°C) for GTD-111 and a high temperature solution treatment 2175°F (1190°C) prior to the partial solution and aging treatments. Microstructure and creep test results of these heat treated specimens revealed that the high temperature solution treatment was necessary to recover the microstructure and properties of in-service degraded GTD-111 DS buckets.

The production of bladed structures, e.g. turbine and compressor wheels, is a subject of statistical scatter. The blades are designed to be identical but differ due to small manufacturing tolerances. The manufacturing tolerances may lead to difference in shape, mass and stiffness distribution of the turbine blades. But it can also take effect on in-homogeneities in the material, which are caused by the casting process and can, for example, reflect in residual stresses and grain size differences. These properties can lead to so called mistuning that increases vibration amplitudes compared to the ideal tuned case, which can end in critical vibration conditions. The object of this study is to determine the main source of mistuning for casted turbine wheels in automotive turbocharger applications. The authors have shown in context of a study on mistuning modeling for turbine wheels in automotive turbochargers, that the mistuning due to the geometrical deviation of the shape is not necessarily solely the main mistuning source. To examine this, various numerical models were evaluated, but also measurements during operation and standstill condition were carried out. Casted turbine wheels with different grain structures and also milled turbine wheels from forged round blanks were analyzed. Besides these, FE-models from casting simulations were used to analyze residual stress and material property effects on mistuning. For the milled turbine wheels the source of the mistuning could be assigned to the deviation of the blade shape. The source of mistuning for the casted turbine wheels, however, could be attributed to the material in-homogeneity.

The geometric parameters of manufactured compressor blades do not exactly comply with the design intention. These deviations result from the abrasion of the forging and milling machines as well as variations of the material properties or the blank part geometries. Using probabilistic methods, the geometric deviations can be considered within the design process. This paper presents the results of a probabilistic High-Cycle-Fatigue investigation under consideration of the geometric parameter scatter of the entire compressor blade. Based on a previous paper of the authors, the geometric parametrization as well as the process chain to apply the geometric scatter to an existing FE-mesh was supplemented by the radii and the geometric dimensions of the compressor blade root. Thus, the impact of all geometric parameter scatter on the High-Cycle-Fatigue strength, the eigenfrequencies and the mode shapes can be evaluated.

The paper presents results of development of the novel shrinkage-free, adaptable to machining and easily welded alumo-boron-carbide silicon materials that experience the cermet stage during their manufacturing. A specific feature of the like ceramics is their double-stage sintering process when, after the original stage, a metal-ceramic blank has a sufficient strength and is easily machined by conventional metal-cutting tools. In addition, such materials are electrically conductive, therefore, the elasto-erosion treatment technique can be applied. Subsequently, a machined part is finally sintered, whereas all the geometries remain actually unchanged due to the shrinkage absence. Prior to the final sintering, all separate parts can be joined by the diffusion welding with the seam strength being 5–10% different from the strength of the main part. The paper provides an insight into the processes and results of tests of the representative selections of samples of four types of the structural ceramics that are experiencing the cermet stage during the process of their formation. Also, ceramic parts for the CGTE hot passage are demonstrated.

Development and testing of gas turbine quality high temperature silicon nitride (NT154) components will be described. An advanced CNC green (using pressed powder blanks prior to densification) machining based complex shape forming methodology has been developed and successfully deployed to fabricate gas turbine quality rotor, vane ring and shroud components to net shape with high yield and required dimensional tolerances. Utilizing a systems approach involving green blank properties, type of cutting tools and machining parameters, the process has been optimized to achieve required as machined surface finish, dimensional control and part integrity. Integral bladed micro turbine rotors (IBR) and vane rings have been fabricated with dimensional control within 100 microns, surface finish within 1–2 microns. IBRs so formed have been successfully spin tested at room temperature at 40% above designed speed approaching maximum stress in the vicinity of 400 MPa.

Burst tests were performed on Ceramic Matrix Composite (CMC) vane specimens, manufactured by two vendors, under the Ultra Efficient Engine Technology (UEET) project. Burst specimens were machined from the ends of 76mm long vane sub-elements blanks and from High Pressure Burner Rig (HPBR) tested specimens. The results of burst tests will be used to compare virgin specimens with specimens that have had an Environmental Barrier Coating (EBC) applied, both HPBR tested and untested, as well as a comparison between vendors.