The effect of nitrogen pressure on in situ combustion synthesis AIN-ZrN composites
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I.
INTRODUCTION
ALUMINUM-nitrogen has drawn great attention over the past decade for its structural applications, due to its low thermal expansion, high thermal conductivity, excellent ballistic impact resistance, low density, and low specific modulus.[1] Its potential applications, however, are limited by its lack of toughness and reliability.[2] A substantial improvement in toughness can be achieved with the incorporation of other phases, by taking the superimposed effect of the properties of these phases.[3] In this article, combustion synthesis (CS) for the fabrication of AlN-ZrN composites is reported, which offers some unique advantages such as cost-effectiveness, low energy consumption, process simplicity, self-purification, high sintering activity, etc.[4] Fabrication of nitrides such as Si3N4,[5,6,7] TiN,[8,9,10] and AlN[11,12,13] by CS technologies has attracted the interest of many scientists and engineers, while CS of AlN-ZrN has rarely been investigated, except in a recent publication about the phase formation and thermodynamic analysis of CS Al-Zr-N composites.[14] It is well known that the mechanical properties of a material are significantly affected by its microstructure. Controlling the microstructures of the combustion product is a key step in applying the CS process. Because nitrogen pressure plays a very important role in the entire process of combustion reaction for solid-gas reaction systems, the effect of nitrogen pressure on the combustion behavior will be discussed in this article, and the observation of the microstructure of the combustion product will be reported. II.
EXPERIMENT
The initial powder, with the characteristics shown in Table I, was mixed and ball milled for 8 hours according to the composition listed in Table II. The powder mixtures were loosely compacted into the porous crucible and then put into a CS chamber pumped to a vacuum of 1024 MPa. The mixed powder was ignited by passing a 20 A electrical
K.X. CHEN, Senior Lecturer, is with the Department of Materials Science and Engineering, Tsinghua University, Beijing, 100084, People’s Republic of China. C.C. GE, Professor, and J.T. LI, Assistant Professor, are with the Laboratory of Special Ceramic & Powder Metallurgy, University of Science and Technology Beijing, Beijing, 100083, People’s Republic of China. Manuscript submitted September 30, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
current through a tungsten coil at nitrogen pressures of 1, 5, and 10 MPa, respectively. Variation of the temperature during the combustion reaction was measured by using W/3 pct Re-W/25 pct Re thermocouples that were directly embedded in the samples, with the voltage output monitored via a computer and data acquisition system. The microstructure of the combustion product was observed using scanning electron microscopy (SCAN360 (Cambridge S-360, England)). III.
RESULTS AND DISCUSSION
The experimental results show that nitrogen pressure has no influence on the phase composition of the combustion products. No other phase was identified
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