Oxide Dispersion Strengthened Copper Alloy Research Articles

Fabrication of Oxide Dispersion Strengthened Copper Alloy Powders by Atmosphere-Controlled Gas Atomization

Fabrication of Oxide Dispersion Strengthened Copper Alloy Powders by Atmosphere-Controlled Gas Atomization

Deformation and fracture behaviour, and thermal stability of ODS-Cu/ODS-Cu and SUS/ODS-Cu joints fabricated by advanced brazing technique

A joint of oxide dispersion strengthened copper alloy (ODS-Cu; GlidCop®), i.e., GlidCop®/GlidCop® joint and a joint of stainless steel (SUS) and GlidCop®, i.e., SUS/GlidCop® joint were prepared by using the advanced brazing technique (ABT). Deformation and fracture behavior, and thermal stability of these joints were investigated by means of three-point bending test, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Firstly, in the case of the GlidCop®/GlidCop® joint, plastic deformation occurred predominantly in the diffusion layer with lower hardness. The fracture proceeded approximately at the center of the diffusion layer. In the case of the SUS/GlidCop® joint, on the other hand, plastic deformation occurred widely in the bulks, GlidCop® and SUS near the interfaces between the bulk and the bonding layer. The fracture proceeded mainly along the interface between the bonding layer and the bulk GlidCop®, and substantially along the interface between the bonding layer and the bulk SUS. Secondly, influences of 2nd-step heat on the GlidCop®/GlidCop® and SUS/GlidCop® joints were examined from viewpoints of microstructure and mechanical strength. Almost no obvious changes in the width of the diffusion layer (GlidCop®/GlidCop® joint) or the bonding layer (SUS/GlidCop® joint), and in the element distribution in these layers after the 2nd-step heat were recognized. In addition, any obvious changes in the shape of stress-strain curve and yield strength were not recognized for both joints.

Advanced multi-step brazing for fabrication of a divertor heat removal component

The advanced fabrication method named advanced multi-step brazing (AMSB) has been developed for fabrication of a tungsten (W)/copper alloy divertor heat removal component in a fusion reactor. The principle of AMSB is repetitive application of the advanced brazing technique (ABT). The ABT was originally developed in our previous work for jointing of W and oxide dispersion strengthened copper alloy (ODS-Cu: GlidCop®) with the BNi-6 (Ni-11%P) filler material. The special feature of the AMSB is that the leak-tight joint of GlidCop® (GlidCop®/GlidCop®) and of stainless steel (SUS) and GlidCop® (SUS/GlidCop®) can be realized by application of the ABT. Therefore, the AMSB enables production of a leak-tight sealing structure with the appropriate lid material such as GlidCop® or SUS for a pre-processed rectangle-shaped cooling flow path channel. The rectangle-shaped cooling flow path channel has an advantage regarding its heat removal capability. Another special feature of the AMSB is that the physical properties of the AMSB joint has strong tolerance against the repetitive brazing heat cycle. Thus, repetitive application of the ABT does not cause any undesired effects on the leak tightness of the GlidCop®/GlidCop® and the SUS/GlidCop®. The new AMSB type component with the rectangle-shaped fluid flow path and the V-shaped staggered rib structure were successfully produced; therein a pre-processed rectangle-shaped cooling flow path channel was sealed with a GlidCop® and SUS lid structure with leak-tight conditions. The component showed excellent heat removal capability under reactor-relevant conditions with ∼30 MW m−2.

Application of the Advanced Multi-Step Brazing for fabrication of the high heat flux component

A novel fabrication method for a divertor heat removal component with tungsten (W) armour and copper alloy heat sink was newly developed and named as the “Advanced Multi-Step Brazing (AMSB). The basic principle of multi-step brazing is to apply the “advanced brazing technique” repeatedly during the manufacturing process of the single divertor heat removal component. The advanced brazing technique was originally developed by our previous work for joining between oxide dispersion strengthened copper alloy (ODS-Cu) and W with BNi-6 (Ni–11%P) filler material. The applied ODS-Cu was GlidCop® (Cu-0.3wt%Al2O3). One of the possible examples of the AMSB fabrication process can be considered as follows. First, an appropriate cooling flow path channel is processed into a GlidCop® heat sink. Then, the flow path channel is sealed in a leak tightness condition with a lid made by GlidCop®. The leak tightness joint between GlidCop® (GlidCop®/GlidCop®) can be realized by application of the “advanced brazing technique.” Second, in order to facilitate the weldability to connect the other cooling pipe system, the sleeves made by stainless steel (SUS) are jointed on the interface edge of the flow path channel of the GlidCop® heat sink with a leak tightness condition by the “advanced brazing technique.” Finally, W armour is jointed on the GlidCop® heat sink also by the “advanced brazing technique.” In this study, the mechanical strength of the SUS/GlidCop® joint was confirmed by the three-point bending test. Then, AMSB divertor mock-up with leak tightness condition was successfully produced.

Leak tight joint procedures for ODS-Cu/ODS-Cu by the advanced brazing technique

The joint of the oxide dispersion strengthened copper alloy, ODS-Cu (ODS-Cu/ODS-Cu), was prepared. The applied ODS-Cu was GlidCop® (Cu-0.3 wt%Al2O3). The joint procedures were based on the brazing technique between GlidCop® and tungsten (W) with BNi-6 (Ni-11%P) filler material. This method was performed without compressive load and without any intermediate layer, and was named the advanced brazing technique. In this study, first, the joint GlidCop®/GlidCop® was prepared without any compressive load. The joint was subjected to the three-point bending test, the Vickers hardness test, microstructure observation and the leak tightness test. The yield strength of the joint was approximately one-half of that of the GlidCop® bulk. In addition, the joint was not leak tightness against fluids. Next, the joint was prepared with compressive load of ˜0.54 MPa which was applied in the direction perpendicular to the joint interface. The yield strength of the joint was almost as high as that of the GlidCop® bulk. Furthermore, the joint achieved leak tightness against fluids. The special feature of this joint method is that a limited volume of the GlidCop® surfaces near the bonding interface are melted during the bonding heat treatment phase at 960 °C due to the eutectic reaction of the Cu-P system. Then, after finalizing the solidification, a tight bonding layer are created without any cavities and cracks. This phenomenon seems to resemble a micro scale welding. The present brazing technique can promise fabrication of a high heat flux component with a complex shaped fluid flow path system with leak tightness.

Deformation and fracture behavior of the W/ODS-Cu joint fabricated by the advanced brazing technique

In our previous work, the joint between oxide dispersion strengthened copper alloy (ODS-Cu), GlidCop® (Cu–0.3 wt%Al2O3) and tungsten (W) demonstrated superior fracture strength (∼200 MPa). This joint was fabricated by the direct brazing method between W and ODS-Cu using BNi-6 (Ni–11%P) filler material without any intermediate layer. This method was named as the improved or the advanced brazing technique. In the present study, deformation and fracture behavior of the joint after the three-point bending test was investigated. At first, it was found that the crack initiation points were dominantly in the W bulk, although it was not clear that the crack initiated from grain boundary or not. Secondly, the crack propagation proceeded mostly in the W bulk but tended to deflect towards the bonding layer. These results interpret the strength of the bonding interface is superior and the present bonding technique is applicable for severe environments such as a high heat flux divertor component on the fusion reactor. Based on the above physical and technological understanding, we successfully fabricated the large scale divertor mock-up which has twenty-eight plates of W with each size of 20 × 20 × 5 mm3.

Microstructure and mechanical properties of mechanically alloyed ODS copper alloy for fusion material application

Advanced oxide dispersion strengthened copper alloys are promising structural materials for application in divertor system of future fusion reactors due to high irradiation resistance, high thermal conductivity, and good mechanical properties. In this study, a new ODS copper including 0.42wt%Y2O3 nanosized oxide particles was developed successfully by mechanical alloying method using addition of 1 wt% Stearic acid in Ar atmosphere. Mechanical alloying resulted in decrease of crystallite size to 28 nm in concurrent with increment of dislocation density and hardness to the saturated level of 1.7×1015m−2 and 226HV0.1 after 48 h milling, respectively. Consolidated ODS copper by SPS and then hot roll-annealing at 900 °C/60 min showed an average grain size of 1.1 µm with a near random texture. Furthermore, TEM observations demonstrated fine semicoherent Y2O3 oxide particles distributed with a misfit parameter (δ) of 0.17 in copper matrix with an average size of 10.8 nm and interparticle spacing of 152 nm. Finally, tensile test evaluation determined comparable mechanical properties of the annealed ODS copper (Cu-0.42wt%Y2O3) with Glidcop-Al25 including a yield strength of 272 MPa and total elongation of 12%, by two mechanisms of grain boundary strengthening and oxide particle strengthening.

Fabrication of divertor mock-up with ODS-Cu and W by the improved brazing technique

Copper alloy has been considered as a divertor cooling tube or heat sink not only in the helical reactor FFHR-d1 but also in the tokamak DEMO reactor, because it has a high thermal conductivity. This work focused on applying an oxide dispersion strengthened copper alloy (ODS-Cu), GlidCop® (Cu-0.3 wt%Al2O3) as the divertor heat sink material of FFHR-d1. This alloy has superior high temperature yield strength exceeding 300 MPa at room temperature even after annealing up to ~1000 °C. The change in material properties of Pure-Cu, GlidCop® and CuCrZr by neutron irradiation are summarized in this paper. A primary dose limit is the radiation-induced hardening/softening (~0.2 dpa/1–2 dpa) which has a temperature dependence. According to such an evaluation, the GlidCop® can be selected as the current best candidate material in the commercial base of the divertor heat sink, and its temperature should be maintained as close as possible to 300 °C during operation. Bonding between the W armour and the GlidCop® heat sink was successfully performed by using an improved brazing technique with BNi-6 (Ni-11%P) filler material. The bonding strength was measured by a three-point bending test and reached up to approximately 200 MPa. Surprisingly, several specimens showed an obvious yield point. This means that the BNi-6 brazing (bonding) layer caused relaxation of the applied stress. The small-scale divertor mock-up of the W/BNi-6/GlidCop® was successfully fabricated by using the improved brazing technique. The heat loading test was carried out by the electron beam device ACT2 in NIFS. The mock-up showed an excellent heat removal capability for use in the FFHR-d1 divertor.

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.

Anisotropy effects on the tensile and fatigue behaviour of an oxide dispersion strengthened copper alloy

In this study, the mechanical behaviour of the GlidCop® AL-15, an oxide dispersion-strengthened (ODS) copper, is investigated. As the extrusion process leads to a morphological and crystallographic texture, specimens are loaded in a parallel or transverse direction to the extrusion direction. Higher monotonic mechanical strength is observed when the loading axis is parallel to the extrusion direction. Under cyclic loading, the material is more prone to cyclic hardening-softening behaviour and exhibits higher fatigue resistance in the extrusion direction than in the transverse one.

Microstructural features and properties of high-hardness and heat-resistant dispersion strengthened copper by reaction milling

The oxide dispersion strengthened copper alloys are attractive due to their excellent combination of thermal and electrical conductivities, high-temperature strength and microstructure stability. To date, the state-of-art to fabrication of them was the internal oxidation (IO) process. In this paper, alumina dispersion strengthened copper (ADSC) powders of nominal composition of Cu-2.5 vol%Al2O3 were produced by reaction milling (RM) process which was an in-situ gas-solid reaction process. The bulk ADSC alloys for electrical and mechanical properties investigation were obtained by sintering and thereafter hot extrusion. After the hot consolidation processes, the fully densified powder compacts can be obtained. The single γ-Al2O3 phase and profile broaden effects are evident in accordance with the results of X-ray diffraction (XRD); the HRB hardness of the ADSC can be as high as 95; the outcomes should be attributed to the pinning effect of nano γ-Al2O3 on dislocations and grain boundaries in the copper matrix. The electrical conductivity of the ADSC alloy is 55%IACS (International Annealing Copper Standard). The room temperature hardness of the hot consolidated material was approximately maintained after annealing for 1 h at 900 °C in hydrogen atmosphere. In terms of the above merits, the RM process to fabricating ADSC alloys is a promising method to improve heat resistance, hardness, electrical conductivity and wear resistance properties etc.

The microstructural evolution of precipitate strengthened copper alloys by varying temperature irradiation

To investigate the effect of varying temperature irradiation on oxide dispersion strengthened copper alloy (GlidCop CuAl15), heavy ion irradiation was carried out by using 2.4 MeV Cu ions up to 30 dpa in the temperature range of 473–673 K. TEM observation of CuAl15 before irradiation showed high density of small alumina particles and dislocations. After 30 dpa at 673 K constant temperature irradiation, voids were formed. However, voids formation was strongly depended on grain size. On the other hand, by a varying temperature irradiation, the number density of voids was decreased as compared with that of 673 K constant temperature irradiation. The result of CuAl15 is consistent with our previous studies of pure copper irradiated under same irradiation conditions.

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.

The tensile deformation, cyclic fatigue and final fracture behavior of dispersion strengthened copper

The tensile deformation, cyclic stress response characteristics, cyclic stress–strain response, cyclic strain resistance and fatigue properties of an oxide dispersion strengthened copper alloy were studied over a range of cyclic plastic strain–amplitudes. The specimens were cycled using tension-compression loading under total strain–amplitude control. In the as-drawn condition, the dispersion strengthened copper alloy displayed continuous softening to failure at all cyclic plastic strain amplitudes. The rolled plus heat-treated microstructure displayed initial hardening followed by rapid softening to failure. The strain–fatigue life relationship is predicted using the parameters obtained from the fatigue test. Potential mechanisms controlling the stress response and concomitant cyclic strain resistance and cyclic fatigue life are also evaluated, and rationale for observed behavior is discussed in light of concurrent and interactive influences of initial state of the matrix dislocation arrangement, magnitude of cyclic strain amplitude, response stress and intrinsic microstructural effects.

Influence of deformation processing on tensile response of dispersion strengthened copper

The influence of deformation processing on microstructure, tensile deformation, and fracture behaviour of an oxide dispersion strengthened copper alloy is presented and discussed. The strength of the alloy, in both the drawn and extruded microstructural conditions, decreased with an increase in test temperature. At a given temperature, the strength of the drawn microstructure was superior to that of the extruded counterpart. For both the drawn and extruded microstructures, the alloy maintained a high value of yield strengthultimate tensile strength ratio. The tensile fracture behaviour of the alloy was identical for both the drawn and extruded microstructures. Tensile deformation was essentially by inhomogeneous planar slip in the copper matrix and at locations remote from the dispersoid particles.

Tensile deformation and fracture behavior of an oxide dispersion strengthened copper alloy

Dispersion strengthened copper has recently emerged as a potentially viable and attractive engineering material for applications requiring high strength, high thermal and electrical conductivities and resistance to softening at elevated temperatures. In this paper, the microstructure, tensile deformation and fracture behavior of an oxide dispersion strengthened copper alloy is examined. The strength of the dispersion strengthened microstructure decreases with an increase in temperature with a concomitant improvement in ductility. The alloy microstructure maintains a high value of yield strength/ultimate tensile strength ratio. The factors contributing to increased strength and the mechanisms governing quasi-static fracture characteristics are examined in light of intrinsic microstructural effects and deformation characteristics of the matrix.

Fracture toughness of copper-base alloys for fusion energy applications

Oxide-dispersion strengthened copper alloys and a precipitation-hardened copper–nickel–beryllium alloy showed a significant reduction in toughness at elevated temperatures (250°C) as compared to room temperature. This decrease in toughness was much larger than would be expected from the relatively modest changes in the tensile properties over the same temperature range. However, a copper–chromium–zirconium alloy strengthened by precipitation showed only a small decrease in toughness at the higher temperatures. The embrittled alloys showed a transition in fracture mode, from transgranular microvoid coalescence at room temperature to intergranular with localized ductility at high temperatures. The Cu–Cr–Zr alloy maintained the ductile microvoid coalescence failure mode at all test temperatures.

High strain cyclic fatigue and fracture of an oxide dispersion strengthened copper alloy: Srivatsan, T.S., Anand, S. and Troxell, J.D. Eng. Fract. Mech. (Sept. 1993) 46 (2), 183–198

High strain cyclic fatigue and fracture of an oxide dispersion strengthened copper alloy: Srivatsan, T.S., Anand, S. and Troxell, J.D. Eng. Fract. Mech. (Sept. 1993) 46 (2), 183–198

High strain cyclic fatigue and fracture of an oxide dispersion strengthened copper alloy

The cyclic strain resistance and fracture behavior of an oxide dispersion strengthened copper alloy are studied. The alloy was cyclically deformed over a range of strain amplitudes giving lives of less than 10 4 cycles to failure. The specimens were cycled using tension-compression loading under total strain control. The alloy displayed combinations of cyclic hardening and softening to failure. The observed cyclic hardening and softening behavior is a mechanical effect and attributed to concurrent and competing influences of dislocation accumulation and dislocation-microstructure interactions. The alloy followed the Coffin-Manson relationship and exhibited a single slope for the variation of cyclic plastic strain amplitude with reversals to failure. Heat treatment was observed to improve cyclic ductility. The low-cycle fatigue properties and fracture behavior of the alloy are discussed in terms of competing and synergistic influences of cyclic plastic strain amplitude, response stress, intrinsic microstructural effects and macroscopic aspects of fracture.

Irradiation performance of oxide dispersion strengthened copper alloys to 150 dpa at 415°C

Results have been obtained on the post-irradiation properties of various oxide dispersion strengthened copper alloys irradiated from 34 to 150 dpa at 415{degrees}C in the Fast Flux Test Facility. The GlidCop alloys strengthened by Al{sub 2}O{sub 3} continue to outperform other alloys with respect to swelling resistance, and retention of both electrical conductivity and yield strength. Several castable ODS alloys and a Cr{sub 2}O{sub 3}-strengthened alloy show increasingly poor resistance to radiation, especially in their swelling behavior. A HfO{sub 2}-strengthened alloy retains most of its strength and its electrical conductivity reaches a constant level after 50 dpa, but it exhibits a higher residual radioactivity.