The powder processing methods including powder metallurgy (P/M) and powder injection molding (PIM) techniques for tungsten (W)–rhenium (Re) were employed to produce a W–Re rocket nozzle. The composition of W–Re was determined by 25 wt.% of Re to avoid the formatting brittle sigma ( σ ) phase. The samples for analysis of the densification behavior on sintering were prepared by die pressing and cold isostatic pressing (CIP). The feedstock for the PIM process was produced by mixing the W–25 wt.% Re powder and binder system based on a wax-polymer with an optimum solid loading through the twin-extruder mixer. The injection molded specimens were debound to extract and decompose the binders via the solvent and thermal debindings. The debound samples were sintered in a hydrogen atmosphere. After sintering, hot isostatic pressing (HIP) was carried out in an argon atmosphere to enhance the density. The dilatometry experiments were performed to analyze and predict a densification behavior during sintering. The master sintering curve (MSC) model was used to characterize the densification behavior with a minimal set of preliminary experiments. The mechanical properties were evaluated through microstructure and chemical composition measured by EDX–SEM and X-ray diffraction (XRD). Finally, the eroding test was conducted using the W–25 wt.% Re rocket nozzle produced by PIM under the high temperature. After carrying out erosion tests, the erosion rate, hardness and microstructure were evaluated.

Development of non-eroding rocket nozzle throat for ultra-high temperature environment

A compact and continuous rhenium coating with black appearance was obtained on the surface of graphite substrate in chloride molten salts with high efficiency and low cost. The rhenium coating prepared at a cathodic current density of 50mA/cm 2 at 850 °C has a preferential growth orientation of 〈110〉 and a high deposition rate of ~ 40 μm/h. The rhenium coating is composed of a fine equiaxed-grain zone and a spired columnar-grain zone. The surface emittance is as high as 0.73, which is comparable with black rhenium coating reported by Ultramet. The microhardness of the coating as deposited is 350 ± 16.4 kg/mm 2 . The bond strength of rhenium/graphite interface tested at room temperature is ~ 10.2 MPa and is greatly improved after heat treatment at 1200 °C for 3 h in vacuum.

Black rhenium coating prepared on graphite substrate by electrodeposition in NaCl-KCl-CsCl-K2ReCl6 molten salts

Mechanical Properties and Thermal Shock Resistance of Rhenium Coating in Iridium/Rhenium/Carbon-carbon Composites

This study investigated the densification behavior of rhenium alloys including W-25 wt.%Re and Re-2W- 1Ta (pure Re) during sintering. The dilatometry experiments were carried out to obtain the in-situ shrinkage in H2 atmo- sphere. The measured data was analyzed through shrinkage, strain rate and relative density, and then symmetrically treated to construct the linearized form of master sintering curve (MSC) and MSC as a well-known and straightforward approach to describe the densification behavior during sintering. The densification behaviors for each material were ana- lyzed in many respects including apparent activation energy, densification parameter, and densification ratio. MSC with a minimal set of preliminary experiments can make the densification behavior to be characterized and predicted as well as provide guideline to sinter cycle design. Considering the results of linearized form and MSC, it was confirmed that the W-25 wt.%Re compared to Pure Re is more easily densified at the relatively low temperature.

Densification Behavior of Rhenium Alloy using Master Sintering Curve

Study of Refractory Materials Usage in Aerospace Engines Technology

: Vacuum Plasma Spray techniques (VPS) have been developed to reduce the cost and fabrication time of metal and ceramic rocket engine components. Refractory metals and ceramics such as Re, Hf, W, W/Re, HfC, and HfN are being used for their high melting temperatures and chemical stability. However, the difficulty of forming these materials into complex shapes has limited their application in the past. The VPS technique involves spraying material onto a mandrel of the desired shape and subsequently removing the mandrel. A primary advantage of VPS forming over other powder metallurgy techniques is that near-net-shape spray forming of components significantly simplifies and reduces the cost of fabrication due to the high material utilization and reduction of laborious machining. Rocket nozzles have been fabricated and successfully tested in advanced applications with zero erosion. Standard metallurgical techniques have been used to characterize the effect of processing parameters on the microstructure of spray formed deposits. The deposited materials have high density with fine grain microstructures.

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Arvind Argarwal

Papers

Low Cost, Net Shape Fabrication of Rhenium and High Temperature Materials for Rocket Engine Components