Oxygen Free High Conductivity Research Articles

Enhancing the detection efficiency of the 3D positive ion detector

Enhancing the 3D positive ion detector's efficiency is the objective of this study. The detector finds numerous applications in the fields of radiation biology, radiation dosimetry, radiation protection, radiation measurement etc. Generally, in 3D positive ion detector the cathode used is either high resistive glass or gold coated over ceramic glass. The detector efficiency has been reported as 2%max with high resistive glass cathode material and 9.2%max with gold coated ceramic glass. In the present study, we have significantly improved the detection efficiency by replacing these materials with an oxygen-free high conductivity (OFHC) copper cathode. This modification resulted in a substantial increase in the detector efficiency, reaching a maximum of 31.3%max. The study also presents a comparison between this enhanced performance and the previously reported efficiencies demonstrating the effectiveness of using high conductivity materials to improve ion detection capabilities.

Modeling and Prediction of Surface Roughness in Ball End Milling of Oxygen-Free High Conductivity Copper Using Adaptive Neuro Fuzzy Inference System

Oxygen Free High Conducting Copper (OFHC) is one of the reasons materials for numerous applications due to its high thermal conductivity, great machinability, and great quality In this paper, an adaptive neuro-fuzzy inference system (ANFIS) is developed as a predicting model of the machining performance of OFHC measured for surface roughness in terms of process parameters, namely, the cutting feed rate or feed per tooth, axial depth of cut, radial depth of cut, and the cutting speed.

Development of high impact toughness Cu/ODS-Cu joints using HIP bonding process for the preparation of W/Cu/ODS-Cu monoblock divertor

Compared to CuCrZr, oxide dispersion strengthened copper alloy (ODS-Cu) exhibits higher stability of properties under irradiation and exposure to elevated temperatures, demonstrating broad application prospects in divertor components. Oxygen-free high thermal conductivity copper (Cu-OFHC) has been frequently employed as an interlayer between W and Cu-based alloy in the fabrication of W/Cu divertor components. This study investigates the effect of joining temperature together with the addition of a Ni interlayer on the interface microstructure and mechanical properties of the Cu-OFHC/ODS-Cu joints. As the joining temperature increased from 680 ℃ to 900 ℃, the interface bonding ratio of the Cu-OFHC/ODS-Cu joints improved from 40.4% to 95.8%, and the impact toughness increased from 23.4 J/cm2 to 133.1 J/cm2. With the addition of a Ni interlayer, the interface bonding ratio increased from 40.4% to 90.3%, and the impact toughness improved from 23.4 J/cm2 to 122.5 J/cm2. Increasing the joining temperature or adding a Ni interlayer effectively reduced interfacial voids, enhanced the interface bonding ratio, and consequently improved the impact toughness of Cu-OFHC/ODS-Cu joints. Then, the W/Cu/ODS-Cu monoblock mock-ups with good interfacial bonding were successfully fabricated under two conditions: at a joining temperature of 900 ℃ without an interlayer and at 680 ℃ with a Ni interlayer. These results provide a fundamental understanding for achieving high-quality Cu-OFHC/ODS-Cu joints and offer technical support for the engineering preparation of W/Cu/ODS-Cu components in future fusion devices.

Numerical and experimental investigation into tool-workpiece interaction in flexible abrasive tool finishing

The present work examines the finishing performance of oxygen-free high conductivity (OFHC) copper using a fabricated flexible abrasive tool. It is challenging to finish soft materials like copper and aluminium using traditional finishing techniques due to frequent scratching. Flexible finishing tool can protect the surface integrity of the workpiece samples during finishing action. Flexible abrasive tools are fabricated using solvent casting method. This method fabricates the flexible tools with homogeneous abrasive dispersion and an open-cell porous structure. The developed tool is self-sharpening and self-lubricating and can finish soft materials efficiently. The flexible abrasive tools can be fabricated in different shapes and sizes to finish internal features and complex shapes. The interaction between the tool and workpiece is examined by the forces exerted by the flexible tool on the workpiece. The areal surface roughness of the finished surface is reduced to 33 nm from its initial roughness of 937 nm after 20 min of finishing a pre-defined region. Theoretical analysis is carried out to estimate contact pressure using Hertz contact theory. The results obtained from numerical and theoretical analysis have a close correlation with the experimental results. The maximum deviation of peak contact pressure obtained in theoretical estimation and numerical analysis from experimental results is found to be 20.73 % and 12.83 %, respectively. As the model includes the basic physics of the tool-workpiece interaction, the results can be improved with the inclusion of micro-level analysis of fluid-filled flexible abrasive tools with embedded abrasives.

Laser Powder Bed Fusion Additive Manufacturing of Mo and TZM Exoskeleton with Cu Infiltration for New Heat Sinks Configuration

This study reports the fabrication and characterization of molybdenum (Mo) metal and titanium‐zirconium‐molybdenum (TZM) alloy exoskeletons with honeycomb cavity structures (HCS) that are infiltrated with oxygen‐free high conductivity (OFHC) Cu under an inert atmosphere as a potential replacement for Cu‐Mo‐Cu laminate in heat sink applications for power electronics semiconductors like GaAs. The thermal expansion behavior and the thermal loading of the starting Mo and TZM structures, and of the Cu‐infiltrated parts are evaluated. The fabricated Mo and TZM structures with density >99% and Mo‐based heat sinks with improved CTE (6.6 × 10−6 K−1) when compared to conventional Cu‐Mo‐Cu laminated heat sinks (CTE = 7.6 × 10−6 K−1). The new Mo and TZM structures promise superior performance due to their closer CTE to that of GaAs and similar semiconductors (CTE = 5.7 × 10−6 K−1). Exposure to temperatures up to 1073 K did not affect the Mo microstructure due to the inherent resistance to recrystallization, while exposure to 1373 K did reduce hardness. In contrast, TZM exoskeletons showed resistance to recrystallization even at 1373 K. The fabricated composite heat sinks showed thermal diffusivity (≈61 × 106 m2 s−1) that is within the upper limits of those reported for commercial laminated heat sinks (45 to 65 × 106 m2 s−1).

Secondary electron yield (SEY) evolution of laser processed oxygen-free high conductivity copper induced by different ultrasonic cleaning durations

Laser treated material surface has highly regular curves and greatly reduces the secondary electron yield of surface. As one of the most typically used materials in the vacuum system of particle accelerators, the surface of oxygen-free high conductivity copper (OFHC) is processed by laser. Moreover, ultrasonic cleaning can effectively remove powders and impurities produced by laser ablation. The secondary electron yield (SEY), surface morphology and surface composition of laser treated oxygen-free copper samples before and after ultrasonic cleaning were compared. Experiments were conducted by using the secondary electron yield test device, X-ray diffractometer, X-ray photoelectron spectroscopy, and scanning electron microscope to characterize the SEY, crystal structures, surface composition and surface morphology of laser-treated oxygen-free copper samples, respectively. The SEY evolution of the samples was investigated and analyzed at electron doses of 7.6 × 10−6 C mm−2: after 15-min ultrasonic cleaning, the δmax of sample #1, #2 and #3 increased from 1.09, 1.23, and 1.38 to 1.19, 1.2, and 1.63, respectively, with the maximum increase of 18.12 %. Ultrasonic cleaning could greatly reduce the accumulation of spherical particles and the fibrous or flocculent structures produced by laser processing, thereby reducing the capture of secondary electrons.

Thermal Design of the Conduction-Cooled High Temperature Superconducting Magnet for Pulsating Magnetic Field

A conduction-cooled high temperature super-conducting (HTS) solenoid is fabricated to produce pulsat-ing 4 T magnetic field for magnetic refrigeration. HTS con-ductor of 245 m is wound as a solenoid with 112 layers each of which consists of 12 turns of the conductor. For a stable ramping operation of the magnet, AC loss inside the wind-ing pack should be effectively rejected to the heat sink. The thermal drains are inserted between the layers and con-nected to the magnet flange which is cooled by a commercial two-stage Gifford-McMahon cooler. They are made of Ox-ygen-Free High Conductivity (OFHC) copper, and has a width of 6 mm and a thickness of 50 μm. Thermal analysis is conducted to confirm the effect of the thermal drain on the AC loss heat rejection. AC loss of the magnet is esti-mated by using T-A formulation (current vector potential T and magnetic vector potential A). The ramp rate of the mag-net and the heat sink temperature are set to 0.1 T/s and 4.5 K, respectively. In the thermal diffusion calculation, each winding layer is considered as the lumped capacitance. In addition, thermal conduction between the adjacent lay-ers and that through the thermal drains are considered. The thermal analysis confirms that the conductor temperature of the winding is maintained lower than the operating limit of 20 K. Based on the results of the thermal analysis, the stable pulsating operation of the conduction-cooled super-conducting magnet is predicted to be feasible and is also confirmed by the experiment.

Quantification of softening kinetics in cold-rolled pure aluminum and copper using High-Temperature Scanning Indentation

The High-Temperature Scanning Indentation (HTSI) method enables the continuous monitoring of various mechanical properties, including Young's modulus, hardness, and creep properties, during specific thermal cycles. In this study, the HTSI method is applied to cold-rolled samples of commercially pure aluminum and oxygen-free high conductivity (OFHC) copper. The observed variations in hardness during heating are attributed to the underlying restoring mechanisms, namely static recovery and static recrystallization. Inverse analyses are performed using established metallurgical models of restoration. The results highlight the influence of the initial deformation state and heating rate on the kinetics parameters. The findings are further supported by Electron-Back Scattering Diffraction measurements. The study concludes by demonstrating the HTSI method's capability to quantify restoration parameters as a function of temperature through a limited number of well-designed HTSI experiments.

A multi-length-scale investigation of the applicability of ductility laws for annealed and work-hardened copper

Small-scale mechanical testing provides unique advantages over conventional testing in investigating the mechanical response of nuclear materials. While small-scale testing enables accelerated materials research, it raises the question of comparability to large-scale properties for engineering design considerations. Among different mechanical properties for structural design considerations such as yield and ultimate tensile stress, ductility is of critical importance with respect to structural component health. The effectiveness of using small-scale mechanical testing for probing these mechanical properties is dictated by understanding how the mechanical responses translate from the microscale to the engineering scale. Therefore, a better understanding of size scaling effects via gathering and analysis of experimental data is required to bridge length-scales. This work builds upon previous reports to provide statistical data on how mechanical response changes as the size of the specimens are reduced from conventional sizes. One hundred twenty mesoscale tensile coupons of oxygen-free high thermal conductivity (OFHC) copper in work-hardened and annealed state have been manufactured using micro-wire electrical discharge machining (EDM) and tested under uniaxial tension. The mesoscale specimens have dimensions dictated by pre-selected geometric ratios (i.e., gauge section length over the square root of the cross-section area) with gauge length dimensions of 3 mm (or less) and sub-millimeter gauge widths and thicknesses. The mesoscale responses were compared to bulkscale properties to reveal the effect of specimen size on the mechanical response as a function of grain size and material state for a single phase face-centered cubic metal.

Investigation of thermal contact conductance of bare copper-copper and aluminum 1070-aluminum 1070 interfaces at low temperatures between 10 and 70 K

The prediction model of thermal contact conductance (TCC) for bare OFHC-OFHC and Al 1070-Al 1070 flat interfaces is presented. OFHC (Oxygen free high conductivity copper) and Aluminum are widely used in cryogenic systems. Since the thermal conductivity of pure copper or aluminum materials has a highly non-linear characteristic with its peak value at around 20 K, it is difficult to predict TCC of those materials at this temperature range. The TCC model in this paper proposes the dimensionless correlation through 16 experiments considering various conditions such as surface roughness, materials, pressure, and temperature. The model has been established by the modification on the previous CMY (Cooper, Mikic, Yovanovich) model with additional parameters. The first important feature of the model is to adopt the contact thermal conductivity (kc). It can be calculated by using the size effect theory at the micro-scale contact single spot. The second feature is the dimensionless temperature (T/TD). An experimental setup is constructed inside of the conduction-cooled cryostat to measure the thermal conductivity of bulk material and the TCC simultaneously for the temperature range between 10 K and 70 K. OFHC and Al 1070 specimens with various surface roughness are prepared and tested with contact pressure of 6 to 13.5 MPa in vacuum environment. The predicted TCC by the proposed model shows a reasonable agreement with the experimental results in low temperature.

Numerical and experimental study of influence function in magnetorheological finishing (MRF) of freeform surface

In the present work, a dynamic viscosity model is proposed based on the varying magnetic flux density of the neodymium permanent magnet along its width. The proposed viscosity model is helpful in analysing the influence function in a better way as compared to standard non-Newtonian fluid models. During the finishing process, the research of influence function aids in establishing the right range of process parameters. MR fluid flow on the freeform surface is examined numerically and experimentally to better understand the influence function. The flow behaviour of the MR fluid is investigated using the three-dimensional (3D) computational fluid dynamics (CFD) simulation, wall shear stress and dynamic pressure are estimated on the Oxygen-free high conductivity (OFHC) copper for various process parameters (working gap and rotational speed). On the convex and concave sections of a freeform surface, indentation depth is estimated for various process parameters using the results of dynamic pressure and empirical relation. Finishing tests are performed to investigate forces (tangential and normal) and indentation depth on the workpiece, and the results are evaluated.

Case study of advanced processed OFHC copper by dry sliding wear test

The wear behaviour of copper material processed by ECAP (Equal Channel Angular Pressing) and orbital forging (OF) is presented in this study. Dry sliding wear tests were carried out for the wear behaviour of the investigated system. Oxygen-free high thermal conductivity (OFHC) copper was used for testing. The new combination of metal forming processes was used because of ease of fabrication. Additionally, wear rate, friction coefficient and wears mechanisms were observed. The friction resistance is caused by the destruction of the adhesion between surface asperities in metal friction. Moreover, increased asperity interactions connected with wear particle entrapment gradually increase the friction coefficient. These results show the metal forming process's positive influence in reducing interfacial adhesion and asperity deformation. Finally, the combinations of newly used advanced processing demonstrated excellent wear characteristics of copper.

Finishing performance of polyurethane-based flexible tools fabricated using solvent casting and particulate leaching method

Oxygen-free high thermal conductivity (OFHC) copper is a common material for mirrors in different optical applications. As it is a soft material and easy to scratch, the nanofinishing using traditional finishing processes is difficult. A flexible abrasive tool that can adapt to the shape of the component and apply uniform and gentle pressure is required to achieve a high-quality surface finish on the soft materials. Flexible abrasive tools are fabricated using the solution casting and dissolution method with open porous microstructure and uniformly dispersed silicon carbide particles in a polyurethane polymer matrix. Mechanical and finishing characteristics of the fabricated tools are obtained under dry and wet conditions. The developed tools are self-lubricating and self-replenishing, reducing tool wear and eliminating burn marks on finished surfaces. Scanning electron micrographs and energy dispersive spectroscopy are used to investigate the tool microstructure and abrasive particle distribution before and after finishing. The mechanical behaviour of tools is studied using a dynamic mechanical analyser. Porosity is measured using the interconnected void volume, and fluid absorption rate is calculated through weight measurement before and after fluid absorption. The surface finish of finished surfaces is analysed using an optical surface profilometer. Results show that the flexible abrasive tool performs the best under wet conditions. In a single pass, a wet salt-leached tool achieved a reduction of 42.2 % on a surface having a lower initial roughness, whereas a wet pure polymer tool achieved a reduction of 45.7 % on a surface having a higher initial roughness. Finally, areal surface roughness of 34 nm is achieved in 16 mins of finishing experiment using pure polymer tool followed by salt-leached tool.

Performance of micro-beam X-ray absorption spectroscopy at beamline 7.2W of Synchrotron Light Research Institute

The existing BL7.2W beamline at SLRI, initially developed for Macromolecular Crystallography, was upgraded with a Si-drift X-ray detector, sample micro-stage, and polycapillary X-ray lens to provide possibilities for experiments using X-ray fluorescence (XRF) imaging and micro-beam X-ray absorption spectroscopy (μXAS) techniques. The micro X-ray beam was characterized. The beam diameter of approximately 25 μm was determined from the knife-edge scan method. The measured photon flux was 3.8 × 109, 1.8 × 109, and 6.4 × 108 photons/s for 8.0, 10.0, and 12.0 keV X-rays, respectively. Imaging XRF and μXAS measurements were successfully performed on a welding joint of oxygen-free high thermal conductivity copper and AISI304 stainless steel. This opens opportunities for SLRI users to utilize this new measurement setup for elemental and chemical characterizations of small areas on various samples.

Dynamic indentation testing and characterization of metals based on the split Hopkinson pressure bar (SHPB) device

The classical quasi–static indentation testing theory and technique have been developed to a relatively mature degree, while the related studies on dynamic indentation testing and characterization are relatively few and incomplete but of significant importance in the actual conditions subjected to local dynamic loading. In this study, a dynamic indentation test device is established based on the split Hopkinson pressure bar test system. The “three–wave method” is proposed and validated through numerical simulations to effectively acquire the dynamic indentation response data (indentation depth and indentation load) of metallic materials, and dynamic indentation tests are carried out on the representative metal of oxygen free high conductivity copper (OFHC) with different striker velocities. Combining the dynamic indentation contact stiffness analysis with related indentation testing theory, the real–time dynamic indentation hardness of OFHC during the loading stage under different striker velocities are determined and certain rate sensitivity is shown. Related research lays a foundation for further studies on dynamic indentation testing and characterization of metals.

Grain size dependence of modified material constitutive model for OFHC copper

Grain refinement occurs during manufacturing process, and grain size has a significant impact on mechanical properties. It is essential to establish the relationship between grain evolution and plastic behavior. The quasi-static and dynamic compression experiments for three kinds of oxygen-free high-conductivity (OFHC) copper with different grain sizes have been carried out. The true stress–strain curves were corrected to the isothermal curves, in which the temperature dependence of the specific heat capacity was used. It was found that the grain size has a significant influence on the yield stress, strain rate sensitivity, and thermal softening. A new phenomenon-based constitutive model considering the grain size and the coupling between strain hardening and strain rate was developed, and the results of the quasi-static and dynamic compression experiments were used to fit the parameters. The experimental data and the predicted results of the newly developed constitutive model agree well, which proves the constitutive model has a high prediction accuracy. The fitted constitutive model depicted that the strain rate sensitivity increases and thermal softening degree declines as the rise of the grain size of OFHC copper. The developed constitutive model could be used to the numerical simulation for the manufacturing process of OFHC copper considering the grain refinement.

Finishing of OFHC copper using fluid filled open-cell porous flexible abrasive impregnated tools

Super finishing of oxygen-free high thermal conductivity (OFHC) copper disks is of great interest as copper is widely used material for high power rated mirrors in laser and other optical systems. It is difficult to super finish copper using traditional finishing processes as it is soft and can be scratched easily. Flexible tools that conform to component shape and maintain low as well as uniform pressure are needed for finishing of soft materials. In this work, open-cell porous flexible abrasive tools are developed using solvent casting method with polyurethane as the base polymer and SiC particles as abrasives. The open-cell porous tools are saturated with deionized water before use. The tools are self-replenishing as the abrasives are uniformly dispersed in the tool and the fluid trapped in pores acts as coolant as well as lubricant. The viscoelastic behavior of the fabricated tools with different abrasive concentrations is characterized using a dynamic mechanical analyzer (DMA). Spot finishing experiments are carried out to optimize the tool RPM, tool compression, and abrasive concentration for better surface finish. The average areal surface roughness (Sa) of copper disk reduced to 54 nm from 946 nm.

Outgassing rate testbed for in-operation analysis of powered and heated assemblies

We introduce a new apparatus for measuring the outgassing rate of assemblies and functional units. Outgassing rates given in the literature, if available, are mostly insufficient to plan and set up a vacuum system, more so if commercial parts, preassembled items, or complex electronics with unknown components are deployed. Outgassing rates have a severe impact on the required pumping speed in ultrahigh vacuum systems and they change if the samples are powered or heated. The newly built apparatus uses the throughput method to measure outgassing rates. It can house probes with a size of 0.10×0.10×0.13m3 and supplies electrical currents of up to 5 A. In addition, a heater can establish temperatures of up to 200 °C directly. A procedure is given to identify the main gas inputs and to retrieve data with a lower limit of 1.5×10−8Pam3s−1 after 100 h in vacuum. In this paper, we present the experimental setup and first results for samples of polytetrafluorethylene, polyamide (PA6), Viton (1A), and oxygen-free high thermal conductivity copper at room temperature.

Influence of Material Microstructure on Machining Characteristics of OFHC Copper C102 in Orthogonal Micro-Turning

Micro-cutting is different from conventional cutting in its mechanics. The workpiece material is not considered to be homogeneous in the micro-cutting process. As a result, it is critical to comprehend how microstructure affects surface integrity, cutting forces, and chip formation. In this paper, we experimented with micro-turning on oxygen-free high-conductivity (OFHC) copper with different microstructures after annealing. Feed rate parameters were smaller than, larger than, and equal to the grain size, respectively. Experimental results show that when the feed rates are equivalent to the grain size, the surface roughness of the machined surface is low and the width of the flake structure on the free surface of chips is minimal, and the explanations for these occurrences are connected to dislocation slip.

Shock initiation of low density polymer bonded explosive LX-14: A study of two morphologies

A series of six shock initiation experiments have been carried out on low density LX-14 powder in order to simulate a shock insult on the heavily damage polymer bonded explosive, LX-14. Two distinct morphologies were studied (tap density molding powder and machined swarf), both at the same density of 0.942 g/cm3, or 50.1% theoretical maximum density. The purpose of these experiments was to provide data to help make an assessment of the effects that damage has on the material sensitivity to a planar shock. This was achieved primarily by providing shock sensitivity data in the form of a Pop plot, and also reactants equation of state data, which aids in the determination of input conditions for both the experiments performed in this work and also future experiments of this material type. The experiments were of a cut-back format, consisting of four sample heights on each shot and diagnosed with optical velocimetry. The experiments were carried out at the Technical Area 40 Chamber 9 gas gun facility at the Los Alamos National Laboratory, where the LX-14 targets were subjected to Al 6061 and Oxygen Free High Conductivity copper impactors launched to velocities up to 2.14 km/s. Time corrected reactive growth wave profiles are presented in this paper along with the derivation of the following Hugoniot parameters for this explosive, where the molding powder and machine swarf are represented by the following linear equations, respectively, US=1.64(±0.64)up+2.25(±0.49) and US=0.87(±0.60)up+4.08(±0.49). The results show that the steady increase in shock sensitivity with increasing void fraction reaches an inflection point beyond which the shock sensitivity begins to decease. This inflection point lies between 65% and 50% of the theoretical maximum density of the LX-14. In both cases, the damaged LX-14 was not as sensitive as expected, with a relative shock sensitivity of the molding powder being less than the pressed LX-14, and the machined swarf having a shock sensitivity that is comparable to pressed LX-14.