Study of the role of Fe and Sn additions in the microstructure of Nb–24Ti–18Si–5Cr silicide based alloys

Study of the effect of Cr and Ti additions in the microstructure of Nb–18Si–5Ge based in-situ composites

“…The data is presented using the parameter C Si max À C Si min [20]. The data shows that Ti in synergy with Ge increased the macrosegregation of Si (compare alloys ZF1 and ZF3).…”

“…It has been shown that formation and stability of equilibrium Nb 3 Si (tP32, prototype Ti 3 P) depends on the synergy of alloying elements and on cooling rate [2,4,14e25]. Metastable Nb 3 Si can also form at low vol% in specific parts of as solidified Nb-silicide based alloys [16,20] and in some cases metastable Nb 3 Si can be stable after exposure to elevated temperatures [20]. It should be noted that the tetragonal Nb 3 Si and tetragonal Nb 5 Si 3 silicides (equilibrium silicides, bNb 5 Si 3 , tP32, prototype W 5 Si 3 , aNb 5 Si 3 , tP32, prototype Cr 5 B 3 ) have nearly identical lattice parameters, and many of the inter-planar spacings and angles closely match those of the metastable A15 Nb 3 Si and that in [16,20] the identification of metastable Nb 3 Si was done on the basis of the chemical composition of the silicide and data in [13] as it was not possible to find Nb 3 Si in thin foils.…”

Ab initio investigation of the Nb–Al system

“…The spatial distribution of the Nb ss and its volume fraction and chemical composition are critical for the properties of Nb silicide based alloys [2][3][4][5][8][9][10]. In these materials creep and high temperature strength and oxidation resistance are provided by the silicide(s) and intermetallic phase(s) and ambient temperature ductility and fracture toughness by the Nb ss , which is expected to impart ductile phase toughening [1,2,11].…”

“…In these materials creep and high temperature strength and oxidation resistance are provided by the silicide(s) and intermetallic phase(s) and ambient temperature ductility and fracture toughness by the Nb ss , which is expected to impart ductile phase toughening [1,2,11]. The chemical composition of the silicides is affected by the alloying additions, for example in Nb 5 Si 3 the Nb can be substituted by Hf, Ti, Mo, W and the Si by Al, B, Ge, Sn [3][4][5][8][9][10][12][13][14] and thus their elevated and ambient temperature properties are also dependent on alloy chemistry [3,[10][11][12][13][14][15].…”

“…Furthermore, even though the maximum solid solubility of Si in Nb is low, the actual Si content in the latter depends on alloy composition and Nb ss with/out Si content can form in the microstructure [5,8,17]. Thus, in Nb silicide based alloys it is possible to have (Nb, TM, RM, simple metal, metalloid) solid solution, (Nb ss ), where TM is transition metal (e.g., Cr, Hf, Ti), RM is refractory metal (e.g., Mo, Ta, W), and the simple metal(s) and metalloid(s) respectively can be Al, Sn and B and Ge [3][4][5][6][8][9][10][11][12][13][14].…”