Analysis of Residual Phases in Nickel Aluminide Powders Produced by Reaction Synthesis
- PDF / 328,320 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 70 Downloads / 194 Views
ANALYSIS OF RESIDUAL PHASES IN NICKEL ALUMINIDE POWDERS PRODUCED BY REACTION SYNTHESIS K. P. MCCOY* , K. G. SHAW** and J. A. TROGOLOt *Xform, Inc. Cohoes, NY "*Xform, Inc. Cohoes, NY t Rensselaer Polytechnic Institute ABSTRACT The use of x-ray diffraction has been used to determine phases present after reaction synthesis of Ni 3 AI powder. The complex diffraction spectra produced by the powder prompted the development of a simulator. The simulator uses nonlinear regression to determine the weight percent of the phases present. The simulator also determines the broadening of each peak in the spectrum. The phases present in Ni 3 AI powder produced by reaction synthesis has been determined with the simulator. The simulator has been used to monitor the progress of phase transformation during various thermal treatments of Ni 3 AI powder. A thermal cycle of 1200'C for two hours has been shown to produce a. phase-pure product. The activation energy for the interdiffusion of nickel and aluminum has been determined to be 260 ± 35 k.1/mole.
INTRODUCTION It is the purpose of this paper to describe a method for determnining the residual phases in powder produced by reaction synthesis. X-ray diffraction was chosen to determine the phases present after reaction synthesis. Ni 3 AI powders produced by reaction synthesis have a multiphase composite nmicrostructure[1]. The phases can have diffraction spectra, with very close or overlapping peaks. Some phases present do not have any unique, non overlapping peaks. This makes the diffraction spectra. of the powders very difficult to interpret. A simulator was developed to model experimental spectra. With this simulator the phases that are present and the weight percent of each phase can be determined. This method has been applied to monitor the progress of a post heat treatment of Ni 3 AI powder. A series of post heat treatments were conducted, the time and temperature dependence of the resulting transformation were determined. To produce internietallic powders by reaction synthesis, it is necessary to control the reaction exotherm. Control of the exotherm can be achieved by heat extraction methods. The result of heat extraction is a. multiphase, composite product that represents the reaction in a transient conditiom[2-9]. In many ways the composite powders produced through controlled reaction synthesis are beneficial. If a ductile material is used as a reactant, this component may be preserved in the composite powder structure resulting in a powder that is easily die-pressed. This is advantageous as very often intermetallic powders are too brittle or hard to effectively shape by die compaction. The concentration gradient present in a composite powder also may aid in sintering by providing a diffusive driving force. In thermal spray applications the lack of phase purity may present problems if a resident phase is lower melting or prone to oxidation. Consequently, it is desirable to determine and control the composition, and phase purity of a. reactively sintered powder, tailoring it t
Data Loading...
