Mechanical Properties of Nb-18Si-5Mo-5Hf-2C <I>In-Situ</I> Composite Prepared by Arc-Casting Method

Abstract

Niobium-base in-situ composite, Nb-18Si-5Mo-5Hf-2C (in mol%), was fabricated by arc-casting method and heat-treated at 2070 K for 20 h in vacuum. The microstructure is composed of Nb solid solution (Nb SS ) matrix phase and secondary phase of Nb 5 Si 3 . The Nb 5 Si 3 was found to have two kinds of structure: one is the α phase reported in the Nb-Si binary phase diagram and the other is a hexagonal phase with Mn 5 Si 3 -type structure. To evaluate the mechanical properties of the composite, nano-indentation hardness tests and tensile tests were conducted. The hardness and elastic modulus at ambient temperature were evaluated using nano-indentation hardness tester and the tensile properties were examined by an Instron-type materials testing machine at temperatures of 300, 1470, 1570, 1670 and 1770 K, and at an initial strain rate of 1 × 10 −4 s −1 . The hardness and elastic modulus of the Nb SS phase are 480 GPa and 170 GPa and those of the silicide are 1480 GPa and 380 GPa. The composite exhibited the excellent ultimate tensile strength of 450 MPa at 1470 K, and the brittle to ductile transition temperature is between 1470 and 1570 K. The fracture behavior of the in-situ composite is complex, however, involving cleavage of the Nb 5 Si 3 , Nb SS /Nb 5 Si 3 interface separation, ductile rupture of the Nb SS and correlations of these.

Nonisothermal and Isothermal Oxidation Behavior of Nb-Si-Mo Alloys

“…The refractory Nb-Si-based alloys with high melting temperatures are of interest as candidate materials for aero-engine applications. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The microstructure of the Nb-Si-based alloys consists of hard and brittle intermetallic Nb 5 Si 3 and relatively ductile Nb-solid solution (Nb ss ) phases. The Nb 5 Si 3 exhibits excellent high-temperature strength retention and creep resistance, [1] but poor ductility and fracture toughness.…”

Evaluation Technique of the Hardness and Elastic Modulus of Materials with Fine Microstructures

“…The estimated elastic modulus in the present study is in good agreement with reported values, which were evaluated for both phases in SMHC18 with an applied load of 9.81 mN in the previous report. 9) Considering that the elastic modulus shows almost no dependence upon the applied load in the nanoindentation tests, E obtained from formula (3) could be regarded as reasonable. The estimated elastic modulus of the Nb 5 Si 3 phase is somewhat greater than that (E % 326 GPa) of monolithic Nb 5 Si 3 fabricated by the powder metallurgy method (P/M).…”

“…In this decade, significant progress has been achieved in understanding the mechanical behavior of Nb-base in-situ composites, such as their high temperature compression properties, 6,7) high temperature tensile properties 8,9) and room temperature fracture toughness. 10) However, there are only a few reports available on the hardness, H, and elastic modulus, E, of the constituent phases of Nb SS /Nb 5 Si 3 in-situ composites, despite of the importance of the property for material design, especially for fracture toughness improvement.…”

Influence of Ni Content on the Microstructure and Dry Sliding Wear Properties of Cr13Ni5Si2/γ Intermetallic Alloys

“…Like the harmful r phase in Ni-base superalloys, martensitic stainless steels, and many other heat-resistant high alloying steels, the single-phase Cr 13 Ni 5 Si 2 is also so brittle that it has little significance for practical applications as a bulk wear-resistant material. It is demonstrated that one of the most effective methods to enhance the toughness and ductility for many intermetallic alloys is the in-situ incorporation of a ductile second phase [14][15][16][17][18] via multicomponent alloying. The Ni-base solid solution (c) is well known for its excellent combination of ductility, toughness, oxidation resistance, high-temperature strength, and corrosion resistance when dissolved with high contents of Cr and Si.…”