Effect of Zirconium on the Densification of Reactively Hot‐Pressed Zirconium Carbide

Abstract

Densification mechanisms involved during reactive hot pressing (RHP) of zirconium carbide (ZrC) have been studied. RHP has been carried out using zirconium (Zr) and graphite (C) powders in the molar ratios 1:0.5, 1:0.67, 1:0.8, and 1:1 at 40 MPa, 800°C-1200°C for different durations. The volume fractions of phases formed, including porosity, are determined from the measured density and from Rietveld analysis. Increased densification with an increasing nonstoichiometry in carbon has been observed. Microstructural and X-ray diffraction observations coupled with the predictions of a model based on the constitutive laws governing plastic flow of zirconium suggest that the better densification of nonstoichiometric compositions arise from the higher amount of starting Zr and also the longer duration of its availability for plastic flow during RHP. Volume shrinkage due to reaction between Zr and C and the gradual elimination of the soft metal phase limit the final density achievable. Based on these observations, a twostep RHP carried out at 800°C and 1200°C leads to a better densification than a single RHP at 1200°C.

Pressureless sintering of ZrC with variable stoichiometry

“…7. Figures 7(a) and 7(b), which are attributed to the sintered sample derived from starting powders of ZrO 2 :C = 1:3.00, do not indicate any extrinsic phase like ZrO 2 or C. This is compatible with the results from the 2 residues could be experimentally proven by investigations with prolonged sintering time. Another observation is the increase of grain size in association with increased sintering temperature for this sample.…”

“…In the past, a combination of very high-temperature with pressure-assisted methods was necessary to produce fully densified ZrC components. Hot pressing is a common method for sintering of ZrC [1][2][3][4][5][6]. Nachiappan et al [4] investigated the influence of Zr and graphite ratio on sinterability.…”

“…Nevertheless, an undesirably exaggerated grain growth occurs with the addition of Zr. Other authors demonstrate an improvement of ZrC sinterability by addition of ZrB 2 and SiC [7][8][9][10]. An alternative sintering method, which enables high densification of ZrC material, is spark plasma sintering (SPS).…”

Effect of nonstoichiometry on mechanical properties of reactive hot‐pressed monolithic ZrCxCeramic

“…One of the reasons for this lack of systematic wear studies is presumably the poor solid‐state sinterability of ZrC; this makes it very challenging to fully densify at low temperatures. In the recent years, significant contributions have been made on reactive hot pressing (RHP) of Zr and C with different molar ratios at moderate temperatures . The monolithic ZrC x ceramic has been produced by RHP of Zr and C powder mixtures at 40 MPa and 1200°C.…”

“…In the recent years, significant contributions have been made on reactive hot pressing (RHP) of Zr and C with different molar ratios at moderate temperatures. [13][14][15] The monolithic ZrC x ceramic has been produced by RHP of Zr and C powder mixtures at 40 MPa and 1200°C. It is also established that the combinations of Zr-B 4 C, Zr-B 4 C-Si, or Zr-B 4 C-SiC powder mixtures, and RHP, results in dense ZrB 2 -ZrC x , ZrB 2 -SiC, or ZrB 2 -ZrC x -SiC composites at 1200-1600°C.…”