Effect of Processing on the High Temperature Mechanical Properties of MoSi 2
- PDF / 291,251 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 37 Downloads / 199 Views
EFFECT OF PROCESSING ON THE HIGH TEMPERATURE MECHANICAL PROPERTIES OF KoSi2 S.N. Patankar and J.J. Lewandowski Dept. of Materials Science and Engineering Case Western Reserve University Cleveland OH 44106 ABSTRACT Polycrystalline MoSi 2 has been processed via spex milling and the notched fracture behavior has been determined at 800 1400 °C. Elemental Mo and Si powders were mechanically alloyed to produce MoSi 2 and were subsequently vacuum hot pressed to fully dense MoSi 2 compacts. Microstructures were analyzed and both hardness and notched fracture tests were conducted at high2 temperatures. The material toughness was constant at 4.5 MPa m" between 800 and 1000 °C, with significant plasticity exhibited at 1200 0C. The results will be compared to recent work on the effects of C on high temperature properties of MoSi 2. INTRODUCTION Molybdenum disilicide is currently being considered as a potential high temperature material because of its high melting point, good strength to density ratio, and its reasonable ductility at high temperatures as compared to other intermetallics and refractory metals. Molybdenum disilicide is often prepared by arc melting or P/M routes, followed by consolidation and sintering at elevated temperatures. In the recent past there has been renewed interest in the development of molybdenum disilicide and molybdenum disilicide based composites with the emergence of more advanced milling and synthesis techniques like spex milling and reaction synthesis [1-7]. Considerable discussion exists as to the brittle to ductile transition temperature, which has been reported as 1000 °C[8J, although recent studies utilizing smooth four point bend tests have indicated that this transition temperature may be as high as 1300 to 1400 °C[91 after certain processing conditions. It is clear that additional studies are necessary to establish the effects of processing conditions on the brittle to ductile transition temperature in MoSi 2 , while lowering the BDTT will improve the performance of MoSi 2 for use as a matrix material whose high temperature strength can be enhanced with suitable reinforcement. The current investigation was conducted to study the high temperature properties of MoSi 2 prepared by spex milling. EXPERIMENTAL PROCEDURE The materials used in the present study were 99.9% pure Molybdenum powder with size range of 3-7 micron and -325 mesh (< 44 micron) pure Silicon powder. A spex mill/model 8000 was used for mechanical alloying. Milling was carried out in a carbidelined steel vial with argon atmosphere to minimize oxidation. The charge to ball ratio was 1:10 while the charge was comprised of 10 grams of powder mixture taken in a proper stoichiometry. The milling was conducted for 3 hours and 13 minutes, followed by xray analysis to determine the reaction products present. The milled powders were subsequently degassed at 800 °C for 6 hours Mat. Res. Soc. Symp. Proc. Vol. 288. 01993 Materials Research Society
830
and hot pressed at 1500 °C for 30 minutes using 51.7 MPa pressure. Hot micro-hardn
Data Loading...
