Systematic investigation of microstructure, distortion, mechanical and thermal properties of NiB and ZrB2-modified 90W-6Ni-4Co alloys.

The present work focuses on the role of NiB and ZrB 2 addition on density, structural evolution, mechanical and thermal properties of 90W-6Ni-4Co (wt%) heavy alloys. The investigated tungsten heavy alloys were sintered at 1485 °C and 1500 °C with a holding time of 75 min in H 2 atmosphere. Compared to the base alloy 90W-6Ni-4Co, the NiB-substituted alloys showed improved densification at both sintering temperatures. An in-depth study of the phase and microstructure of the 1500 °C sintered samples was carried out. X-ray diffraction analysis confirmed the presence of ZrO 2 in ZrB 2 containing WHAs. Microstructural analysis affirms that ZrB 2 incorporation attributes for grain size refinement in sintered alloys. Furthermore, the elephant foot formation in the sintered samples was avoided by incorporating NiB individually or in combination with ZrB 2 dispersoids. The distortion parameter (δ) of the samples sintered at 1500 °C was found to be decreased from 24.83 (0 wt% ZrB 2) to 6.36 (2 wt% ZrB 2). On the other hand, the combined addition of NiB and ZrB 2 provides better shape retention with δ =2.82 for the tungsten heavy alloys with 3 wt% NiB and 2 wt% ZrB 2. The maximum compressive stress of ∼2000 MPa was obtained in the 89W-6Ni-4Co-1ZrB 2 samples. The maximum and minimum bulk hardness of 432 ± 5 HV 3 and 365 ± 9 HV 3 was obtained for 88W-3Ni-3NiB-4Co-2ZrB 2 and 90W-6Ni-4Co heavy alloys. The coefficient of thermal expansion of the 90W-6Ni-4Co alloy was found to be the highest (7.65 × 10−6 /°C), which was reduced to 7.1 × 10−6 /°C and 6.8 × 10−6 /°C with the incorporation of 1 and 2 wt% ZrB 2 respectively. W-rich channels were noticed in the microstructure of 1500 °C sintered samples. Overall, W-Ni/NiB-Co-ZrB 2 alloys are very effective in enhancing the mechanical properties and distortion behavior compared to W-Ni-Co alloys. • ZrB 2 addition refines W grain size in sintered alloys. • XRD and EDS analysis confirm the partial transformation of ZrB 2 to ZrO 2. • A distinct channel like structure was noticed in NiB-substituted sample. • The liquid phase sintered W-Ni/NiB-Co-ZrB 2 alloys prevent shape distortion. • ZrB 2 -containing heavy alloys offer reduced thermal expansion coefficient. [ABSTRACT FROM AUTHOR]