Oxide Dispersion-strengthened Copper Research Articles

Effects of composite oxide addition on the microstructure and properties of ODS copper

Oxide dispersion strengthened copper-based material is widely used in electrical contact materials due to its excellent mechanical and electrical properties. However, researchers have found that large Y2O3 particles have poor interfacial bonding with the copper matrix in the study of oxide dispersion strengthened copper. In this work, Y4Zr3O12 nanoparticles were successfully prepared through solid–liquid doping and directly added into oxide dispersion-strengthened copper by mechanical alloying. A scanning electron microscope, a transmission electron microscope, an X-ray diffractometer, and electrical and mechanical tests were used to characterize the microstructure and performance of composite materials. The interfaces between the Y2O3/Y4Zr3O12 nanoparticles and Cu were systematically studied. The interface bonding between Y4Zr3O12 and Cu was better than that of Y2O3 and Cu. The effect of different Y4Zr3O12 contents (1, 3, and 5 wt%) on the microstructure and mechanical properties of the composites was studied. Results showed that the Cu-3 wt% Y4Zr3O12 composites exhibited the best comprehensive properties. The Vickers hardness, yield strength, ultimate tensile strength, maximum engineering strain, and electrical conductivity of the Cu-3 wt% Y4Zr3O12 composites were 132HV, 203.5 MPa, 284.7 MPa, 15.8 %, and 90.3 % International Annealed Copper Standard, respectively.

The microstructure, mechanical-thermal properties and softening resistance of Y4Al2O9 dispersion-strengthened Cu alloy

Oxide dispersion-strengthened copper (ODS-Cu) alloys with yttrium oxide nanoparticles are promising heat sink materials in fusion reactor due to their high strength, thermal conductivity and thermodynamic stability. The particle size and number density of oxide nanoparticles can be improved via addition of microalloying element. In this study, the atomized Cu-Y alloy, Al and Cu2O were used as the Y source, the microalloying element and the oxidant material, respectively, to fabricate ODS-Cu alloy by mechanical alloying method. After spark plasma sintering and annealing, a ODS-Cu alloy with a microstructure containing Y4Al2O9 nanoparticles homogeneously distributed in Cu(Al) solid solution matrix was successfully fabricated. It is found that a crystallographic orientation relationship of (31¯2)Y4Al2O9∥(11¯1)Cu(Al) was formed between Y4Al2O9 nanoparticles and Cu(Al) matrix and the lattice mismatch was 0.337%. The small lattice mismatch reduced the nucleation barrier for Y4Al2O9 nanoparticles so a mean particle size of 4.8 nm and a number density of 2.16×1024 m−3 were obtained in the alloy. Consequently, the microhardness was enhanced via Hall-Petch strengthening, dislocation strengthening and dispersion strengthening. The softening temperature of ODS-Cu alloy was improved to higher than 1000 °C due to the thermodynamic stability and the pinning effect of Y4Al2O9 nanoparticles. In addition, the thermal conductivity of Cu-1Y-9Al-0.3Cu2O alloy is close to other copper alloys as the volume fraction of Y4Al2O9 nanoparticles is limited. Cu-1Y-9Al-0.3Cu2O alloy provides a good overall performance, which may be used as heat sink materials under severe conditions.

Microstructure development in cryogenically rolled oxide dispersion strengthened copper

Recently, advanced oxide dispersion strengthened (ODS) copper alloys have been developed using mechanical alloying process as a fusion material. In this study, to develop a superior ODS copper alloy containing 0.5wt% Y2O3, the effect of cryogenic rolling on microstructure development and tensile properties was studied using high resolution EBSD, TEM and tensile tests. During cryogenic deformation of ODS copper, grain structure remains in submicron size scale as a combinatorial result of geometrically effects, nanotwin bundle deformation, interaction of dislocations with fine oxide particles and some diffusional processes including static recovery and recrystallization. Clear microstructural characterizations confirmed nucleation of fine new oriented recrystallized grains mainly on the HABs of 80%cryogenic rolled ODS copper. Quantitative analyses indicated grain boundary migration at room temperature following cryogenic deformation originated from high driving force induced by grain boundary bulging and high mobility induced by vacancies. The tensile properties of cryogenic deformed samples showed superior tensile strength than room temperature deformation leading to UTS: 624 MPa, elt: 5.5%, while saturation of strength between 60%-80% reduction, approved occurrence of softening by diffusional processes.

Microstructure and Nano-hardness of Pure Copper and ODS Copper Alloy under Au Ions Irradiation at Room Temperature

The microstructure and nano-hardness of the pure copper and oxide dispersion-strengthened (ODS) copper alloy subjected to 1.4 MeV Au ions irradiation at room temperature were investigated. After irradiation, dislocation-loops form in both materials, while voids can only be generated in the pure copper. Compared with the irradiated pure copper, larger average diameter and lower number density of irradiation-induced dislocation-loops were detected in the ODS copper alloy, revealing that high-density dislocation and large volume of Al2O3 particles existing in the ODS copper alloy can act as effective sinks for the irradiation-induced defects. It was also detected that irradiation hardening in the ODS copper alloy is lower than that in the pure copper. The microstructure and nano-hardness results reveal that the ODS copper alloy has a better irradiation tolerance than the pure copper. In addition, the average diameter of the Al2O3 particles in the ODS copper alloy decreases after irradiation, because the Al–O chemical bonds are decomposed and the atoms are redistributed in the matrix during the irradiation process. This work reveals that the irradiation tolerance of the copper can be effectively enhanced by adding nano-sized Al2O3 particles into the matrix.

Transfer Solid Lubrication of Aluminum Sliding Contacts

The effects of transfer from solid lubricant sticks of unfilled, glass-filled, and bronze-filled PTFE on the room-temperature wear and friction of trailing primary contacts of aluminum (6061 T6) rods in repetitive intermittent contacts were investigated in a ring-on-rod configuration. The materials of the ring countersurfaces upon which the solid lubricants transferred and against which the trailing aluminum rods wore included steel, aluminum, copper, and an oxide dispersion-strengthened copper alloy. This sliding of the unlubricated copper ring countersurfaces against the aluminum led to the roughening of the copper as large (> 1 mm) aluminum particles embedded themselves upon the countersurface, with consequent transitions in the aluminum wear rate and the coefficient of friction to values exceeding 6 × 10− 3 mm3/Nm and 0.6, respectively, after an incubation period of several initial contacts of lower wear rate and friction. The other ring countersurface materials resulted in similarly high aluminum rod wear rate and coefficient of friction, more nearly from the onset of sliding. The application of unfilled PTFE solid lubricant transfer reduced the aluminum's gouging of the copper countersurfaces and correspondingly reduced the aluminum rod wear rate and the coefficient of friction against the copper, as well as against all other countersurface materials, towards 2 × 10−3 mm3/Nm and 0.3 or less, respectively. Glass- and bronze-filled PTFE transfer lubricants provided reductions in the wear rate of the aluminum rod comparable to or in some cases better than the unfilled PTFE, though the unfilled PTFE transfer lubricant in several cases provided better friction reduction.

Microstructure and room temperature hardening of ultra-fine-grained oxide-dispersion strengthened copper prepared by cryomilling

The microstructure of ultra-fine-grained (UFG) oxide-dispersion strengthened (ODS) copper, produced by mechanical alloying at low temperatures (cryomilling) and subsequent hot pressing under protective argon atmosphere of copper powder and 3 vol.% of yttrium and calcium oxides, respectively, was examined by means of high-resolution scanning electron microscopy. Compressive deformation experiments at room temperature yield a substantial increase of the 0.2% yield strength of the UFG ODS copper when compared with pure copper. The very high yield strength ( σ 0.2 = 600 MPa) is the result of a simultaneous occurrence of grain boundary strengthening and particle hardening. The overall yield strength could be best modelled by a linear superposition of the Orowan stress for particle hardening and of the contribution from fine grain strengthening after Hall–Petch.

Creep in ODS copper reinforced with alumina short fibres—DRS copper

Creep in copper dispersion strengthened with fine alumina particles (oxide dispersion strengthened (ODS) Cu) and reinforced with alumina short fibres—a DRS Cu composite—is investigated in two temperature intervals, namely 673–773 K, lower temperature interval (LTI) and 923–1023 K, higher temperature interval (HTI). It is shown that in both intervals creep is associated with true threshold stresses decreasing with increasing temperature more strongly than the shear modulus of copper. The true threshold stress in the composite is higher than that in the composite matrix (i.e. ODS copper) by a factor Λ, by which the flow stress in the matrix is reduced due to load transfer. The minimum creep strain rate is found to be dislocation core diffusion controlled in LTI and lattice diffusion controlled in HTI. High values of the apparent activation energies are fully explained in terms of the temperature dependence of the true threshold stress in LTI as well as in HTI. Also the values of the apparent stress exponents are explained in terms of the true threshold stresses. The true threshold stress is identified with the athermal detachment stress σ d =σ OB 1−k R 2 , and its nonproportionality to the Orowan stress σ OB is explained by the relaxation factor k R increasing with temperature.

Effect of hydrogen on ductility of ODS copper

In oxide dispersion strengthened (ODS) alloys, the oxide/metal interface plays an important role as regards hydrogen trapping which in turn affects the hydrogen embrittlement behavior. In these alloys, the presence of small oxide dispersoids results in a very large matrix/oxide interfacial area that are ideal locations for hydrogen segregation. The aim of the present study is to understand the effect of the matrix/oxide interface on the hydrogen embrittlement behavior of internally oxidized Cu-Al{sub 2}O{sub 3} alloys. This study focuses on the effect of physically stable dispersoids of Al{sub 2}O{sub 3} on the embrittlement behavior unlike the effect of Cu{sub 2}O seen in pure Cu.

Toroidal field system for tight aspect ratio tokamak reactors

A single-turn coil configuration is described with an unshielded central column, which must carry a high current density continuously whilst subjected to high neutron fluxes. A 3-dimensional thermal-hydraulic analysis shows that a current density of 5 kA/cm 2 is practicable whilst 8 kA/cm 2 is possible. A column with a waisted profile is seen to dissipate significantly less power. Oxide dispersion-strengthened copper is found to be the most suitable material for the colum and provides sufficient strength to support the self-forces on the coils. Demountable joints between the column and the parallel return conductors facilitate its annual replacement, which limits the ohmic power dissipation and specific radioactivity. The use of a single-turn coil leads to very high power supply current requirements (typically 6 MA). A power supply with 12 modules positioned around the torus, supplying the magnet in parallel through radial busbars, is proposed. The trade-offs which must be made, if future experimental results indicate that multi-turn coils can be insulated, are discussed.