Recent advances in the simulation of the quench, cold-work and machining processes for large aluminum forgings are opening the way for a new paradigm in the design, manufacture and sustainment of aircraft structures. The use of large forgings permits the unitization of smaller parts (brackets, fittings, lugs, etc.) with primary structural components like spars and bulkheads. This is being done in order to reduce part count, which in turn leads to significant reductions in manufacturing cost. Unitization can also translate into weight reduction / avoidance when comparing against built-up structure, but it raises a number of issues for structural durability and damage tolerance, notably reduced repair / replace capability and reduced crack arrest capability. The viability of the unitization concept is dependent not only on the availability of material systems that retain their mechanical properties in very thick sections, but also on the designer’s ability to retain durability and damage tolerance, and to understand and mitigate the effects of residual stresses.

: A powder metallurgy route based on hot isostatic pressing (HIPing) of tape-cast monotapes was used for the direct fabrication of dense thin sheets of gamma titanium aluminide. Polarized light microscopy revealed a fine-grained microstructure but a few isolated larger grains were also present. The primarily metastable alpha2 microstructure of the rapidly solidified starting powder transformed to the equilibrium near-gamma microstructure during HIPing. Chemical analysis revealed that the dense sheet had a carbon content of 0.13 wt.%, which was only 0.04 wt.% higher than that of the starting powder, but the oxygen content was significantly higher, presumably introduced during the decanning step. The hardness measured using Vickers microindentation technique was 384 +/- 9 HV. Manipulation of the as-HIPed microstructure was performed by heating for up to 1 hour in flowing argon at temperatures below and above the alpha transus. Below 1250 deg C, limited grain growth and no discernable change in the as-HIPed (near-gamma) microstructure occurred.

A powder metallurgy route based on hot isostatic pressing (HIPing) of tape-cast monotapes was used for the direct fabrication of dense thin sheets (250–300 μm thick) of gamma titanium aluminide (γ-TiAl). Polarized light microscopy revealed a fine-grained microstructure (average grain size ~ 3 μm) but a few isolated larger grains (~20 μm) were also present. The primarily metastable α2 microstructure of the rapidly solidified starting powder transformed to the equilibrium near-γ microstructure during HIPing. Chemical analysis revealed that the dense sheet had a carbon content of 0.13 wt.%, which was only 0.04 wt.% higher than that of the starting powder, but the oxygen content was significantly higher, presumably introduced during the decanning step. The hardness measured using Vickers microindentation technique was 384 + 9 HV. Manipulation of the as-HIPed microstructure was performed by heating for up to 1 hour in flowing argon at temperatures (1170-1385C) below and above the alpha transus (1355°C). Below 1250°C, limited grain growth and no discernable change in the as-HIPed (near-γ) microstructure occurred. Sheets heated to 1320°C and 1365°C had a duplex microstructure of γ and α2 grains, with some lamellar grains. Except for a thin surface layer (20–30 μm thick), the microstructure of the heat-treated sheet was uniform, but a fully lamellar microstructure was not achieved even after heating for 1 h at 1385°C.

Thermal barrier coatings (TBCs) made Of Y2O3-stabilized ZrO2 are used extensively to protect and insulate the metallic structure of advanced gas turbine engines. For applications that require prolonged exposure to temperatures above 1000-1200 degrees C, structural changes produced by sintering and phase transformation limit the durability of the coatings. The objective of the present study was to investigate the use of Gd2O3 as an alternative stabilizer for ZrO2-based TBC materials. The influence of Gd2O3 concentration (4-20 mole percent) on the sintering and phase stability of plasma-sprayed ZrO2 powders was investigated and the data were compared with those for Y2O3-stabilized ZrO2. At an equivalent concentration (4 mole percent), Gd2O3-stabilized ZrO2 sintered more slowly but had a lower resistance to destabilization of the metastable tetragonal (t') phase, when compared to Y2O3-stabilized ZrO2. The thermal conductivity of Gd2O3-stabilized ZrO2 was lower than that for Y2O3-stabilized ZrO2. Mechanisms for the effect of Gd2O3 on the behavior of ZrO2 are discussed.

Abstract : The time for structural materials development and use must be shortened (time focus, not cost focus). Industrial M & P community demanding a quantum-leap in relevant engineering simulation capability. Accelerated Insertion of Materials is the long-term, strategically-relevant, computational materials science & engineering vision. Materials Science & Engineering community must produce integrated predictive tools. Accelerated insertion demands integration of engineering design with M & P to achieve true systems engineering of materials technologies.

The effect of heat treatment on the thermal conductivity of plasma-sprayed Y2O3 stabilized ZrO2 (YSZ) and Al2O3 coatings was investigated. A heat treatment of 1300 °C in flowing argon for 50 h was found to significantly increase the thermal conductivity of the coatings when compared to measurements in the assprayed condition. Transmission electron microscopy (TEM) examination of the microstructures of the coatings in the as-sprayed and heat-treated conditions revealed that sintering of microcracks at the splat interfaces was the main cause for the increase in thermal conductivity. In the YSZ coatings, complete closure of microcracks was frequently observed. In contrast, microcrack closure in the Al2O3 coatings was characterized by the isolated necking of particles across a microcrack rather than complete closure. A model for thermal conductivity in a solid containing oriented penny-shaped cracks was used to explain the observed increase in thermal conductivity after heat treatment.

A sensor has been developed and tested that is capable of emitting and receiving ultrasonic energy at temperatures exceeding 900°C and pressures above 150 MPa. The sensor works with standard ultrasonic pulser-receivers and has demonstrated the capability of measuring workpiece deformation during hot isostatic pressing. Details of the sensor design, performance, and coupling of the ultrasound to the workpiece are described. Ultrasonic data acquired by the sensor in-situ during hot-isostatic-pressing runs are presented.

A sensor has been developed and tested that is capable of emitting and receiving ultrasonic energy at temperatures exceeding 900 degrees C (1652 degrees F) and pressures above 150 MPa (22,500 psi). The sensor is based on a unique form of aluminum nitride that retains its piezoelectric properties at high temperatures. The sensor works with standard ultrasonic pulser-receivers and has demonstrated the capability of measuring workpiece deformation during hot isostatic pressing (HIP). Details of the sensor design, performance, and coupling of the ultrasound to the workpiece are described. Ultrasonic data acquired by the Sensor, in situ, during HIP nms and at elevated temperatures in air are presented.

An ultrasonic nondestructive methodology for evaluating the consolidation and microstructure of advanced fiber-reinforced composites has been developed to aid in their design and fabrication. The use of this nondestructive evaluation (NDE) technique can enable optimization of the processing parameters to obtain complete densification around the fibers. In addition, the methodology can be used to ensure that the composite panels are devoid of any global problems such as fiber swimming, ply delamination, embedded manufacturing anomalies such as voids, etc. Such a post processing NDE is also essential before any interfacial characterization is performed. The technique described in this paper, being generic, is applicable to both metal matrix and ceramic matrix composites.