SHS-Derived Powders by Reactions' Coupling as Primary Products for Subsequent Consolidation

Abstract

The capability of self-propagating high-temperature synthesis (SHS) to produce powders that are characterized by a high sintering ability, owing to high heating and cooling rates inherent to the exothermic reaction, is of a special interest for the industry. In particular, SHS-derived powders comprise a significant defect concentration in order to effectively enhance the mass transfer processes during the sintering, which allows for the successful consolidation of difficult-to-sinter materials at relatively low sintering temperatures. From this perspective, the design of precursors suitable for sintering, synthesis in a controlled temperature regime and the optimization of geometrical and structural parameters of SHS powders as a potential feedstock for the consolidation is of key importance. Here, we report on the comparative studies concerning the SHS processing of composites for advanced powder metallurgy techniques. The synthesis and sintering peculiarities of the SHS through coupled reactions in the Me'O₃(WO₃,MoO₃)-Me''O(CuO,NiO)-Mg-C, Ti-B-Al₁₂Mg₁₇ systems are comparatively reviewed. The SHS coupling approach was used for the preparation of powders with a tuned degree of fineness (a high specific surface area of particles), a high-homogeneity and a controllable distribution of elements via both the regulation of the thermal regime of combustion in a wide range and the matching of the thermal and kinetic requirements of two interconnected reactions. Microstructural features of the powder feedstock greatly contributed to the subsequent consolidation process.

Keywords: combustion synthesized powder; mechanical properties; microstructure; self-propagating high-temperature synthesis; sintering; thermal coupling.

Figure 1

Thermodynamic modelling of WO₃-CuO-yMg-xC, WO₃-NiO-yMg-xC and MoO₃-CuO-yMg-xC systems and XRD patterns of the products (W-Ni (a), W-Cu (b) and Mo-Cu (c)) at optimum conditions, P = 0.3 MPa.

Figure 2

Combustion temperature profiles of the CuO + MoO₃ + 1.2Mg + xC mixtures, x = 0 (a), x = 5.0 (b), CuO + MoO₃ + C (c) (Q₁ and Q₂ are the amount of heat released). P_N2 = 0.3 MPa.

Figure 3

Combustion temperature (T_c) and combustion velocity (U_c) vs. carbon content in the WO₃-CuO-1.3Mg-xC, WO₃-NiO-1.7Mg-xC and MoO₃-CuO-1.2Mg-xC systems. P = 0.3 MPa.

Figure 4

SEM images of SHS-derived W-Cu powder (a,b) and SEM/EDS of fracture surface of HEC counterparts (c,d).

Figure 5

SEM/EDS of SHS-derived W-Ni composite powder after acid leaching (a,b), XRD pattern (c) before (1) and after SPS (2), SEM of surface of SPS-produced bulk sample, 5 min, 1200 °C (d).

Figure 6

SEM images of fracture surface of SPS produced samples, (a) 3 min, (b) 10 min, T = 1200 °C.

Figure 7

EDS mapping of fracture of the Ni-W SPS-produced sample, 5 min, 1200 °C (a), W (b), Ni (c), W, Ni (d).

Figure 8

SEM of Mo-Cu powders obtained by different pathways (a,d,g); SEM images after SPS of samples fracture and surface of Cu-Mo obtained from SHS + SCS pathway (b,c); Cu-Mo obtained from SHS of oxides (e,f); Cu-Mo obtained from SHS of CuMoO₄ salt (h,i); T = 950 °C, P = 100 MPa, t = 6 min, d = 10 mm.

Figure 9

SEM images of SHS powder (a) and dense samples sintered by SPS at 1450 °C (b). Reprinted from Nikitin et al., 2020 with copyright permission, Ceramics International [38].

Figure 10

Plots of hardness and relative density values for the systems under consideration; W-Cu (a,b), W-Ni (c,d), Mo-Cu (e,f), AlMgB₁₄-TiB₂ (g,h).