Interfacial characterization of SLM parts in multi-material processing: Metallurgical diffusion between 316L stainless steel and C18400 copper alloy

Selective laser melting (SLM) is a metal additive manufacturing (AM) technique that can fabricate complex parts of any shape. In this paper, the interfacial microstructure and mechanical properties of 316L/CuSn10 bimetallic structure were studied, and the ability of self-developed multi-material SLM equipment to form multi-material bimetallic structures was described. The investigations of 316L/CuSn10 bimetallic structure involved microscopic features, phase analysis, microhardness, tensile properties and bending properties. Moreover, the mechanical properties of multi-material specimens were compared with that of single material samples. In addition, scanning electron micrograph shows that the width of the bimetallic fusion zone is about 550 μm, and dendritic crack sources was found on the boundary between the bimetallic fusion zone and the steel region. In the direction perpendicular to the interface, the Vickers microhardness value gradually changed from 233.1 ± 8.1 HV in the steel zone to 154.7 ± 6.0 HV in the bronze zone. The non-standard tensile samples were printed and tested for evaluating tensile properties, the ultimate strength of 316L/CuSn10 joint was 423.3 ± 30.2 MPa comparing with the 316L stainless steel of 673.1 ± 4.2 MPa and the CuSn10 Tin-bronze of 578.7 ± 30.6 MPa. Tensile stress-strain curves and fracture characteristics show that the fusion zone of steel and bronze exhibits brittle fracture mechanism. Furthermore, three-point bending test was used to evaluate the interfacial bonding strength of the bimetallic structure, and results show that the maximum flexural strength of 316L/CuSn10 bimetallic structure isn't in middle of but below that of 316L stainless steel and CuSn10 Tin-bronze. The research founding that SLM can obtain 316L/CuSn10 bimetallic structure with good joint strength by adopting island scanning strategy and inter-layer stagger scanning strategy in the interfacial layers.

Interfacial microstructure and mechanical properties of 316L /CuSn10 multi-material bimetallic structure fabricated by selective laser melting

Size-induced enhanced mechanical properties of nanocomposite copper/niobium wires: nanoindentation study

Recently conventional cryochemical processes have been complemented by cryoextraction, cryoprecipitation, cryoimpregnation and freeze casting techniques. Considerably more attention is being paid to colloidal solution processing and the application of sol-gel procedures like ion exchange treatment and hydrolysis of organometallic compounds. New preparation methods for nanopowders of various oxides and metals have been developed while further treatment of cryochemical powders using powder engineering techniques allows the powder grain size to vary from 0.2 to 5-6 µm. Cryochemical methods are also suitable for preparation of various porous media, like porous silica or cryogels with surface areas close to those of aerogels, and for the synthesis of HTSC powders for different applications. Fundamental and applied aspects of cryochemical processing are discussed.

Recent progress in cryochemical synthesis of oxide materials

Bi2Sr2CaCu2Ox(Bi2212)/Ag multifilamentary wires are manufactured via the powder-in-tube process using oxide powders. After deformation, the wires undergo a partial-melt process, resulting in a complex, heterogeneous microstructure containing multiple secondary phases and porosity, limiting the wires? electrical and mechanical performance. Here, an alternative approach using the direct conversion of metallic precursors (MPs) to Bi2212 is studied. The formation of metallic precursor powders via a mechanical alloy is discussed. The MP powder is then converted to superconducting Bi2212 through a simple two-step heat treatment. By introducing oxygen at a temperature at which Bi2212 is in a stable phase, and holding at an elevated temperature for a sufficient time, the metallic precursors are oxidized and transformed into Bi2212. Several factors that impact the formation and growth of Bi2212 grains are discussed. Peak temperature, holding time and heating rate are shown to affect the MP ?Bi2212 conversion, the Bi2201 content and the Bi2212 morphology and density. It is found that Bi2Sr2CuOy (Bi2201) can be the only phase impurity after heat treatment, which is quite different from what is observed in partial-melt processed wires derived from oxide precursors. Lastly, the microstructure at the sample/silver interface suggests larger size and preferred orientation of Bi2212 grains with the aid of a silver surface. Implications for MP Bi2212 wires are discussed.

http://iopscience.iop.org/article/10.1088/0953-2048/27/5/055016/pdf

Synthesis of Bi2Sr2CaCu2Ox superconductors via direct oxidation of metallic precursors

The features of corresponding manufacturing process for Cu–Nb microcomposite wires are presented. Investigation on the influence of the microstructure and crystallographic parameters on strength and conductivity properties of model microcomposite wires and conductors with cross-sections up to 26 mm 2 are presented. The estimation of the potentially achievable mechanical and electrophysical properties of Cu–Nb microcomposite wires has been done. For Cu–Nb wires with 11 mm 2 cross-section the RT ultimate strength 1350 MPa, the RT yield strength 1200 MPa, RRR exceeding 4.6 and conductivity near 65% IACS have been attained.

High strength, high conductivity Cu–Nb based conductors with nanoscaled microstructure

Textured Bi 2 Sr 2 Ca 1 Cu 2 O χ /Ag tapes prepared by “powder-in-tube” method and partial melt process were studied. A new model of texture formation during partial melt technology was proposed for Bi(2212)-Ag composites. The model is based on anisotropic Bi(2212) crystalline growth from melt in quasi-two-dimensional volume and explains a wide set of experimental data. The computer simulation of the growth process according to the suggested model was carried out. The factors promoting the texture increase were revealed.

Texture formation in Bi2Sr2Ca1Cu2Oχ/Ag tapes prepared by partial melt process

Two promising types of Cu/stainless steel (SS) macrocomposite and Cu-Nb microcomposite winding wires for large scaled high field pulsed magnets are reviewed. The estimation of the potentially achievable combinations of mechanical and electrophysical properties has been done. The features of corresponding manufacturing processes for Cu/SS and Cu-Nb wires are presented. The strength-conductivity properties of several types of Cu-Nb and Cu/SS conductors are given. Relationships between the microstructure parameters and mechanical properties of Cu-Nb wires are discussed. The RT (room temperature) ultimate tensile strength at the level of 900-1100 MPa and conductivity 50-60% IACS for Cu/SS conductors with cross-sections up to 40 mm/sup 2/ has been attained. For Cu-Nb wires with 6 mm/sup 2/ cross section the RT ultimate strength exceeding 1400 MPa has been attained.

Cu-Nb and Cu/stainless steel winding materials for high field pulsed magnets

Two promising types of Cu/SS macrocomposite and Cu–Nb microcomposite winding wires for large-scaled high-field pulsed magnets are reviewed. The features of corresponding manufacturing processes for Cu/SS and Cu–Nb wires are presented. It was shown that the manufacturing process designed for the fabrication of composite multifilamentary low-temperature superconducting wires could be successfully applied for the production of high strength, high conductivity Cu–Nb microcomposite conductors. The strength–conductivity properties of several types of Cu–Nb and Cu/SS conductors are given. The microstructure of Cu–Nb microcomposite conductors has been investigated by means of SEM and X-ray analysis. The influence of microstructural parameters on the mechanical and electrical properties has been analyzed. The room temperature (RT) ultimate tensile strength (UTS) at the level of 900–1100 MPa and conductivity 50–60% IACS for Cu/SS conductors with cross-sections up to 40 mm2 have been attained. The strength–conductivity properties of several types of Cu–Nb microcomposite wires with continuous and “in situ” formed discrete filaments are presented. For Cu–Nb “in situ” wires with 6 mm2 cross section the RT UTS exceeding 1400 MPa and conductivity ∼60% IACS have been attained.

High strength, high conductivity macro- and microcomposite winding wires for pulsed magnets

Extremely high strength in microcomposite Cu-Nb wires is associated with ultra-fine-scale microstructure. The extended interfaces between ribbon-like niobium filaments and copper matrix contain the areas of semi-coherent interfaces that are apparently the main reason of significant level of residual stresses observed in microcomposite Cu-Nb wires. The analysis of nonequilibrium of such microstructure has been done. The issue of stability of nanostructured two-phase Cu-Nb materials in the form of winding wires for pulsed magnets has been considered in the present work. The results of measurements of mechanical properties and electrical conductivity carried out on the same samples after periods of time up to 7 years are presented. Different types of Cu-Nb microcomposites with cross sections from 0.07 mm2 to 21 mm 2 were investigated. It was shown that microcomposite Cu-Nb wires maintained essentially unchanged their mechanical and electrical properties after many years aging at room temperature. An analysis has been done on the correlation of the mechanical and conducting properties with microstructure

N.E. Khlebova

Papers

High strength, high conductivity Cu–Nb based conductors with nanoscaled microstructure

Texture formation in Bi2Sr2Ca1Cu2Oχ/Ag tapes prepared by partial melt process

Cu-Nb and Cu/stainless steel winding materials for high field pulsed magnets

High strength, high conductivity macro- and microcomposite winding wires for pulsed magnets

Stability Aspects of the High Strength High Conductivity Microcomposite Cu-Nb Wires Properties