Cr-ni-ti, Fe-ti-si And Co-fe-ta Ternary Alloy Phase Diagram Study

The diffusion couple technique is a convenient, effective andadvanced method used to determine the isothermal section of the ternarysystems, while the traditional method of equilibrated alloys is the mostextensively applied approach in phase diagram determination, which isoften used to confirm or accurately determine the phase equilibriaestablished via the experimental results from diffusion couples. In thispaper, the isothermal sections of the Cr-Ni-Ti ternary system at 927℃,the Fe-Ti-Si ternary system at 900℃and the Co-Fe-Ta ternary system at1100℃have been investigated by combining above-mentioned methods.The following are the main contents:1. The isothermal sections at 927℃of the Cr-Ni-Ti ternary systemThe isothermal section at 927℃of the Cr-Ni-Ti system wasdetermined using a high-efficiency diffusion couple approach,supplemented with 8 equilibrated alloys. Both the diffusion couplespecimens and the alloys were examined by means of optical microscopy,scanning electron microscopy, and electron probe microanalysis. Noternary compound was found. The following five three-phase equilibriawere observed: (1) TiNi₃+(Cr)+(Ni); (2) TiNi₃+(Cr)+TiNi; (3) TiNi+(Cr)+Cr₂Ti; (4)Ti₂Ni+Cr₂Ti+TiNi; (5)Ti₂Ni+Cr₂Ti+(Ti). The solubilities of Cr in NiTi₂, NiTi, and Ni₃Ti were determined to be 7.5,14.5, and 11.4 at.％, respectively.α-Cr₂Ti andβ-Cr₂Ti dissolve about 9.2and 13.9 at.％Ni, respectively.2. The isothermal sections at 900℃of the Fe-Ti-Si ternary systemThe isothermal sections in the Fe-Ti-Si system at 9000℃have beeninvestigated using a FeTi alloy/Si diffusion couple and 25 decisiveternary alloys. The samples are examined by means of optical microscopy,scanning electron microscopy, and energy dispersive spectrometry. Thevarious phases in the alloys annealed at 900℃for 240 hours wereidentified by X-ray diffraction, and the phase equilibrium compositionwere measured by means of energy dispersive X-ray detector. Six ternarycompounds (τ₁: FeTiSi₂,τ₂: FeTiSi,τ₃: Fe_52.0Ti_12.0Si_36.0,τ₄: Fe_10.0Ti_46.0Si_44.0,T₅: Fe_19.0Ti_39.0Si_42.0, andτ₆: Fe_33.0Ti_52.0Si_15.0) were found at thistemperature, and the isothermal section at 900℃are constructed.3. The isothermal sections at 1100℃of the Co-Fe-Ta ternary systemThe phase equilibria of the Co-Fe-Ta ternary system at 1100℃havebeen investigated using five CoFe alloy/Ta diffusion couples and 13decisive ternary alloys. The samples are examined by means of opticalmicroscopy, scanning electron microscopy, and energy dispersivespectrometry. The experimental results show no existence of ternarycompounds at 1100℃. There are four three-phase regions at thisisothermal section, viz.(1)(Ta)+Ta₂Co+TaFe, (2)TaCo+TaFe+Ta₂Co, (3)TaCo+TaFe+Ta(Co,Fe)₂, (4)Ta(Co,Fe)₂+γ-TaCo₂+(Co,Fe). Thecompoundsβ-TaCo₂ and TaFe₂ form continuous solid solutions.