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Kompozyty wolframowe

Ludyński Z., Bucki J.J.

Kompozyty

2004

R. 4, nr 11

243-247

Scharakteryzowano właściwości fizyczne i zakres zastosowań kompozytów wolframowych. Opisano kolejne operacje procesu technologicznego z wyjaśnieniem zjawisk w nich zachodzących. Przeprowadzono badania strukturalne oraz badania właściwości fizycznych stopu o składzie chemicznym 90W-7Ni-3Fe. Wnioski z prac zawierają program badań mających na celu podwyższenie właściwości, zmodyfikowanie technologii oraz rozszerzenie zakresu zastosowań kompozytów wolframowych.

Tungsten composites (often called also tungsten heavy alloys) structure consists of high strength tungsten particles in ductile matrix. The density is in range 17.0-18.6 g/cm2 (due to high 88-98% tungsten content). As-sintered strength 750-950 MPa (with 10-30% elongation) can he increased by work hardening up to 1300-1500 MPa. High purity powders of particle size in range of few [micro]m (FSSS) are used in tungsten composites production process shown in Figure 1. The key part of the production process is occurring below tungsten melting temperature liquid phase sintering, involving a number of diffusion driven phenomena. The process conditions are presented schematically in Figure 2. Typical as-sintered structure for 90W-7Ni-3Fe composite, consisting of spheroidal tungsten grains in the 55Ni-23Fe-22W matrix is shown in Figure 3a. High mechanical properties (ultimate strength 960 MPa, yield stress 680 MPa, hardness 27 HRC) could be further improved by work hardening. It has been shown that tungsten composites (as opposite to pure tungsten) can be processed by cold deformation. Details are given for cold rolling of 25x25x2 mm sample plates after 20 and 40% reduction. The microstructures after rolling are shown in Figures 3b and 3c. Changes of microstructure quantitative parameters measured on parallel and perpendicular sections are presented in Table 1. Samples after rolling have been annealed in nitrogen at 500-750°C. The results of tensile and hardness tests are summarized in Table 2. Tensile properties increase (while elongation quickly decreases) with increasing reduction ratio. Annealing leads to further increase of tensile properties and hardness. The highest ultimate strength of over 1500 MPa (over 60% increase in comparison to as-sintered material) has been received for 40% reduction and annealing at 500-620°C. Conclusions cover propositions of further studies for improvement of alloys properties and modification of technology, as well as extension of application area for tungsten composites.