Plasma Spray Forming Research Articles

Near net shape forming of aluminium matrix composites by thermal plasma spray forming : F. Ajersch et al. J. of Metals, vol 48, no 6, 1996, 56–59

Near net shape forming of aluminium matrix composites by thermal plasma spray forming : F. Ajersch et al. J. of Metals, vol 48, no 6, 1996, 56–59

Plasma spray forming: An alternate route for manufacturing free-standing components

The present study uses plasma spray technology as a production process for the fabrication of free- stand-ing, near- net- shaped NiAl components. Attention is especially focused on the in situ synthesis of NiAl. A new internal, dual powder injector blade has been designed to improve the gun performance as well as the spray efficiency of the feedstock powder. The specific role of the substrate (i.e., its shape and material) for the successful spray forming of free- standing parts is studied. The as- sprayed parts were subjected to a post- heat- treatment and hot isostatic pressing. Subsequently, they were metallographically inspected. The mechanical properties, such as hardness, Young’s moduli, and the fracture behavior during four-point bending, are also examined.

Ductility degradation of vacuum-plasma-sprayed NARloy-Z at elevated temperatures

Vacuum plasma spray forming is being used in the near-net fabrication of aerospace components at the Marshall Space Flight Center (MSFC), Alabama. For example, vacuum-plasma-sprayed (VPS) NARloy-Z (a copper-based alloy with high thermal conductivity) is used to form the combustion chamber liner of liquid rocket engines. VPS NARloy-Z possesses properties comparable with the wrought alloy at temperatures ranging from −259 to 316 °C. However, VPS material exhibits lower ductility than the wrought material at chamber operating temperatures (ranging from 427 to 649 °C). Because of these findings, an investigation was initiated into the mechanisms responsible for the loss of high-temperature ductility. Fracture analysis indicated that ductility loss at elevated temperatures is associated with a transition in fracture mode from transgranular to intergranular. Low-ductility specimens featured extensive grain boundary cavitation with limited grain elongation in the stress direction. Grain size also influenced the high-temperature ductility; finer grained material is more ductile. VPS NARloy-Z had more cavities at grain boundaries and a higher bulk oxygen content than wrought NARloy-Z. The ductility loss at high temperatures appears to have been caused by compounding effects of excessive oxygen and grain boundary cavitation. High-temperature ductility was improved by altering the thermal processing (pre-hot isostatic pressing (HIP) vacuum anneal, HIP and post-HIP vacuum aging) to reduce oxygen and enhance grain boundary integrity.

Vacuum plasma spray forming of refractory metals and ceramics for space furnace containment cartridges—an extended abstract

Tungsten can be VPS formed to 99% density in furnace retort shapes. The VPS tungsten microstructure is dependent on substrate temperature. Material deposited below 815 °C (1500 °F) displayed a splat structure, whereas material deposited above 1150 °C (2100 °F) was recrystallized. The VPS process can be used to make transitions from alumina to a gradient layer with a continuously increasing proportion of tungsten to a pure tungsten layer in a single spray operation.

Metallurgical and process comparison of vacuum plasma spray forming on internal and external surfaces—A technical note

Vacuum plasma spray (VPS) forming is being developed and characterized for near-net-shape fabrica-tion of aerospace components. Applications require VPS forming of structural materials in both mono-lithic form (i.e., freestanding shapes) and as integral parts of complex components (e.g., a liner for a rocket engine combustor). In these applications the material deposited on both the inside and the outside of large and small components must meet strict quality requirements. This paper discusses metallurgical and processing comparisons between depositing material on inside and outside surfaces of symmetrical shapes. Specific examples of material properties (e.g., grain structure, hardness, and tensile properties) and process parameters (e.g., standoff distance and gun design) are discussed in terms of the fabrication of large rocket engine combustion chambers.

Plasma spray forming of intermetallics and their composites\

PLASMA spray processing, a well-established technique for producing protective coatings, is well suited for spray forming applications. It combines the processes of melting, rapid solidification, and consolidation in a single step. Low-pressure or vacuum plasma spraying (VPS) has been widely used for spray forming because it yields dense and relatively oxide-free deposits. During VPS, the deposits undergo continuous annealing due to exposure to high temperatures (>800 ~ This self-annealing is beneficial as it provides stress relief, recrystallization, and enhanced interparticle bonding (Ref 1). The reduction in residual stresses permits the buildup of thick, oxide-free deposits of reactive metals. Thus, VPS can be viewed as a viable technique for consolidation of powders and composites for the production of freestanding deposits of high-performance materials. A key advantage of VPS is the ability to produce rapidly solidified freestanding near-net shapes, thus obviating the need for postspray thermomechanical processing. Chang et al. (Ref 2) have observed that plasma-sprayed nickel-base alloys and intermetallics yield better mechanical properties than melt-spun and hot isostatically pressed materials. In an extensive study undertaken at Stony Brook, Ni3A1, NiAI-Ni3A1, and MoSi2 intermetallics and their composites have been spray formed using VPS processing (Ref 3, 4). The microstructure and room-temperature mechanical properties of the monolithic and composite deposits in the as-sprayed and heat-treated conditions have been examined.

Evaluation of NiAl and NiAl-B deposited by vacuum plasma spray

Nickel aluminide, NiAl, has potential for high-temperature structural applications because of its high melting temperature, low density, high elastic modulus, and excellent oxidation resistance. However, inadequate room-temperature ductility and low strength at high temperatures limit the use of NiAl for practical service. An added limitation is the difficulty of forming this intermetallic compound. Plasma spray forming is suggested to produce NiAl in useful shapes and forms. In this study, vacuum plasma spray has been used to produce coatings and free-standing forms of NiAl and NiAl microalloyed with boron (NiAI-B). This research focuses on an investigation of the structures and properties of the as-sprayed deposits. Preliminary analysis reveals that the deposits formed by vacuum plasma spray are very dense and essentially oxide free. The as-received aluminide powders and the sprayed deposits have the same phase structure. Tests also indicate that the mechanical properties achieved by plasma spray are comparable to those achieved by other processing techniques.

Vacuum Plasma Spray Forming of High Temperature Silicides

AbstractMolybdenum disilicide and its composites have been fabricated by a number of researchers in recent years through vacuum plasma spray (VPS) forming. VPS is capable of producing dense, fine grained deposits of these high temperature intermetallics and is a promising technique for near-net-shape manufacturing. Reviewed here is VPS forming of high temperature silicide intermetallics, principally Mosi2 and its composites. A discussion will be given of the processing-structure-properties relationship of the spray formed silicide.

Plasma spray consolidation of materials

Abstract

Mechanical Properties of Rapidly Solidified Nickel-Base Superalloys and Intermetallics

ABSTRACTThe improvements in the mechanical properties of nickel-base alloys that have been made possible by rapid solidification processing are reviewed. The results of processing by powder metallurgy, laser melting, low pressure plasma deposition and spray forming are examined. In general, the increased homogeneity obtained by rapid solidification allows for increased alloying and improved hot workability. The refined grain size improves the low and intermediate temperature strength, but leads to lower strengths at high temperature. For the high temperature applications, post solidification grain growth is required, as for example the directional recrystallization of powder metallurgy preforms. The development of a novel means of producing a fine dispersion from amorphous alloy precursors and the recent work attempting to improve the ductility of the intermetallic phases NiAl and Ni3A1 are also described.