We realize that the 2.1 deg difference in orientation between the proposed and the Rong/Dunlop OR is small such that the latter might be derived by approximation due to a lack of detailed analysis at the atomic level. However, we cannot agree with the notion that the two are the same because the small angular difference can lead to large lattice strain at the interface with the M 2 C lathes having a finite width (ϳ20 nm, carbides "C" in Figure 2 [1] ), as observed in the present study.The comments on our article raised a good point in that the invariant line approach cannot explain the orientation of the longest axis of the M 2 C precipitates in ferrite. However, it fell short to elucidate the cause of the problem and to distinguish the two (lattice match and invariant line) methods in its argument. The invariant line method is based on the elastic continuum theory. Although the method relies on lattice mismatch data for its predictions, it disregards atomic (lattice point) match in its calculation. This can be readily understood by the fact that an invariant line derived in a lattice transformation is generally not required to coincide with the low-index lattice directions of both phases in question. As a result, it is often ineffective predicting particle orientations in coherent precipitation problems.For this reason, we did not resort to the invariant line approach for the prediction of the longest axis of the M 2 C carbides in our study. Instead, it was concluded that the small lattice mismatch and good atomic registration along the [100] ␣ /[2 0] C common direction controls the primary orientation of the carbide lathes. However, the orientation of the second longest axis of the lathes in the plane perpendicular to the longest axis cannot be determined accordingly. Our study indicated that the invariant line approach could give a satisfactory account of the orientation of the axis. The success could be attributed to the facts that the lattice mismatch in the two perpendicular directions on the (100) ␣ /(2 0) C common plane is very similar and the repeat distance along the two is close.It is understood that there are limitations to both the lattice match and invariant line approaches, [3] and neither could resolve all the orientation issues involved in the present problem alone. The lattice (atomic) match approach is expected to play a major role dominating precipitate orientations. The invariant line approach, on the other hand, becomes valid to the issue of the second axis of the M 2 C lathes when lattice match criterion fails to resolve. This latter orientation problem is nonexistent if the precipitates are viewed to be needle-shaped. Our experiments clearly showed, as well as others, [4,5,6] that the M 2 C carbides in these alloys were lath-shaped. Recent experiments on INCONEL* 718 (IN 718) indicate * INCONEL is a trademark of INCO Alloys International, Huntington, WV.that the yield and subsequent flow stress are significantly higher in compression than in tension [1] over a range of temperatures, exhib...

The flow and fracture behavior of Be-Al alloys were determined in tension with different levels of superimposed pressure. The Be-Al alloys were prepared by Brush Wellman, Inc. (Cleveland, OH) from prealloyed powders processed to either a hot isostatically pressed ("hipped") or cold isostatically pressed and extruded condition. Significant effects of pressure on both the flow and ductility have been observed at room temperature, with implications on the formability of these materials. The effects of changes in processing conditions and stress state on the flow and fracture behavior are summarized in addition to both optical and scanning electron microscopy (SEM) examination of the fracture surfaces. Separate other studies on the alloy constituents (e.g., Al and Be) are also reported. The results are also compared to previous works on monolithic materials and composites tested with high pressure.

The effect of forging pressure on linear friction welding (LFW) behaviour of a single crystal Ni-based superalloy was investigated. Crystal orientations of the specimens were controlled and results indicated that welding success is dependent on proximity of the oscillation direction to the <011> direction. Characterization of the welds included optical examination of the microstructural features of the weld and thermomechanically affected zones (TMAZ) in relation to the parent material. Mechanical properties of the welded material examined via microhardness testing showed an increase in strength in the weld zone (WZ). Microstructural examination indicated that some recrystallization occurred in the WZ, as well as a small amount of distortion of the dendrites in the TMAZ. With increased forge pressure, recrystallized grains remaining in the weld were minimized.

To improve the efficiency of gas turbines, the turbine inlet temperature needs to be increased. The highest temperature in the gas turbine cycle takes place at the exit of the combustion chamber and it is limited by the maximum temperature turbine blades, vanes and discs can withstand. A combination of advanced cooling designs and Thermal Barrier Coatings (TBCs) are used to achieve material surface temperatures of up to 1200°C. However, further temperature increases and materials that can withstand the harsh temperatures are required for next-generation engines. Research is underway to develop next-generation CMCs with 1480 °C temperature capability, but accurate data regarding the thermal load on the components must be well understood to ensure the component life and performance. However, temperature data is very difficult to accurately and reliably measure because the turbine rotates at high speed, the temperature rises very quickly with engine startup and the blades operate under harsh environments. At the operating temperature range of CMCs, typically platinum thermocouples are used, however, this material is incompatible with silicon carbide CMCs. Other temperature techniques such as infrared cameras and pyrometry need optical access and the results are affected by changes in emissivity that can take place during operation. Offline techniques, in which the peak temperature information is stored and read-out later, overcome the need for optical access during operation. However, the presently available techniques, such as thermal paint and thermal crystals cannot measure above ∼1400°C. Therefore, a new measurement technique is required to acquire temperature data at extreme temperatures. To meet this challenge, Sensor Coating Systems (SCS) is focused on the development of Thermal History Coatings (THC) that measure temperature profiles in the 900–1600 °C range. THC are oxide ceramics deposited via air plasma spraying process. This innovative temperature profiling technique uses optically active ions in a ceramic host material that start to phosphoresce when excited by light. After being exposed to high temperatures the host material irreversibly changes at the atomic level affecting the phosphorescence properties which are then related to temperature through calibration. This two-part paper describes the THC technology and demonstrates its capabilities for high-temperature applications. In this second part, the THC is implemented on rig components for a demonstration on two separate case studies for the first time. In one test, the THC was implemented on a burner rig assembly on metallic alloys instrumented with thermocouples, provided by Pratt & Whitney Canada. In another test, the THC was applied to environmental barrier coatings developed by NASA, as part of a ceramic-matrix-composite system and heat-treated up to 1500°C. The results indicate the THC could provide a unique capability for measuring high temperatures on current metallic alloys as well as next-generation materials.

No abstract