Copper alloy composite bit matrix was prepared by pressureless vacuum infiltration,using at least one of the three kinds of tungsten carbide particles,for example,irregular cast tungsten carbide,monocrystalline tungst...Copper alloy composite bit matrix was prepared by pressureless vacuum infiltration,using at least one of the three kinds of tungsten carbide particles,for example,irregular cast tungsten carbide,monocrystalline tungsten carbide and sintered reduced tungsten carbide particles.The effects of powder particle morphology,particle size and mass fraction of tungsten carbide on the microstructure and mechanical properties of copper alloy composite were investigated by means of scanning electron microscopy,X-ray diffraction and abrasive wear test in detail.The results show that tungsten carbide morphology and particle size have obvious effects on the mechanical properties of copper alloy composites.Cast tungsten carbide partially dissolved in the copper alloy binding phase,and layers of Cu_(0.3)W_(0.5)Ni_(0.1)Mn_(0.1)C phase with a thickness of around 8–15μm were formed on the edge of the cast tungsten carbide.When 45%irregular crushed fine cast tungsten carbide and 15%monocrystalline cast tungsten carbide were used as the skeleton,satisfactory comprehensive performance of the reinforced copper alloy composite bit matrix was obtained,with the bending strength,impact toughness and hardness reaching 1048 MPa,4.95 J/cm^(2) and 43.6 HRC,respectively.The main wear mechanism was that the tungsten carbide particles firstly protruded from the friction surface after the copper alloy matrix was worn,and then peeled off from the matrix when further wear occurred.展开更多
Computing the sign of the determinant or the value of the determinant of an n × n matrix A is a classical well-know problem and it is a challenge for both numerical and algebraic methods. In this paper, we review...Computing the sign of the determinant or the value of the determinant of an n × n matrix A is a classical well-know problem and it is a challenge for both numerical and algebraic methods. In this paper, we review, modify and combine various techniques of numerical linear algebra and rational algebraic computations (with no error) to achieve our main goal of decreasing the bit-precision for computing detA or its sign and enable us to obtain the solution with few arithmetic operations. In particular, we improved the precision bits of the p-adic lifting algorithm (H = 2h for a natural number h), which may exceed the computer precision β (see Section 5.2), to at most bits (see Section 6). The computational cost of the p-adic lifting can be performed in O(hn4). We reduced this cost to O(n3) by employing the faster p-adic lifting technique (see Section 5.3).展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52074365)grateful to the Sichuan Science and Technology Program,China(Grant No.2022YFG0289)+2 种基金sponsored by the Funding Project of Key Laboratory of Sichuan Province for comprehensive Utilization of Vanadium and Titanium Resources,China(Grant No.2018FTSZ26)the Project Supported by the Opening Project of Material Corrosion and Protection Key Laboratory of Sichuan province,China(Grant Nos.2021CL26,GK202104,and GK202106)supported by the Ph.D.Programs Foundation of Sichuan University of Science and Engineering,China(Grant No.2021RC18).
文摘Copper alloy composite bit matrix was prepared by pressureless vacuum infiltration,using at least one of the three kinds of tungsten carbide particles,for example,irregular cast tungsten carbide,monocrystalline tungsten carbide and sintered reduced tungsten carbide particles.The effects of powder particle morphology,particle size and mass fraction of tungsten carbide on the microstructure and mechanical properties of copper alloy composite were investigated by means of scanning electron microscopy,X-ray diffraction and abrasive wear test in detail.The results show that tungsten carbide morphology and particle size have obvious effects on the mechanical properties of copper alloy composites.Cast tungsten carbide partially dissolved in the copper alloy binding phase,and layers of Cu_(0.3)W_(0.5)Ni_(0.1)Mn_(0.1)C phase with a thickness of around 8–15μm were formed on the edge of the cast tungsten carbide.When 45%irregular crushed fine cast tungsten carbide and 15%monocrystalline cast tungsten carbide were used as the skeleton,satisfactory comprehensive performance of the reinforced copper alloy composite bit matrix was obtained,with the bending strength,impact toughness and hardness reaching 1048 MPa,4.95 J/cm^(2) and 43.6 HRC,respectively.The main wear mechanism was that the tungsten carbide particles firstly protruded from the friction surface after the copper alloy matrix was worn,and then peeled off from the matrix when further wear occurred.
文摘Computing the sign of the determinant or the value of the determinant of an n × n matrix A is a classical well-know problem and it is a challenge for both numerical and algebraic methods. In this paper, we review, modify and combine various techniques of numerical linear algebra and rational algebraic computations (with no error) to achieve our main goal of decreasing the bit-precision for computing detA or its sign and enable us to obtain the solution with few arithmetic operations. In particular, we improved the precision bits of the p-adic lifting algorithm (H = 2h for a natural number h), which may exceed the computer precision β (see Section 5.2), to at most bits (see Section 6). The computational cost of the p-adic lifting can be performed in O(hn4). We reduced this cost to O(n3) by employing the faster p-adic lifting technique (see Section 5.3).
