Cu-Mo Alloys Research Articles

Effect of Mo nanoparticles on microstructure and mechanical properties of Cu alloys by self-propagating and spark plasma sintering

Cu alloys strengthened with Mo nanoparticle, with Mo contents of 2 at.%, 4 at.%, 6 at.%, 8 at.%, and 10 at.%, were fabricated by self-propagating high-temperature synthesis, followed by two-step hydrogen reduction and spark plasma sintering. The microstructures, mechanical properties, and thermal conductivity of these Cu-Mo alloys were investigated. The results reveal that two-step hydrogen reduction effectively reduces the average Mo particle size to 13.8 nm compared to one-step reduction. With increasing Mo content, the average grain size of Cu initially decreases but then increases due to the segregation of Mo particles. Notably, the Cu-6 at.% Mo alloy exhibits the smallest average grain size of 0.46 μm, with dispersed nanoscale Mo particles of 25.6 nm. The Cu-6 at.% Mo alloy demonstrates superior mechanical properties, with a tensile strength of 405.0 MPa and an elongation of 24.9 %. Furthermore, the Cu-6 at.% Mo alloy has a high thermal conductivity of 320.0 Wm−1K−1 even at 400 °C and a high electrical conductivity of 82.3 % IACS at room temperature. This work offers valuable insights for the design of advanced Cu composites suitable for heat sink applications.

Achieving high-thermal-conductivity brazed joint between carbon-based composites and Mo-Cu alloys by increasing the heat transfer area

Carbon-fiber-reinforced carbon matrix (Cf/C)-Mo30Cu brazed joints play an important role in the cooling systems of thermonuclear reactors. However, the limited contact area of heterogeneous interfaces severely limits the heat transfer efficiency. To overcome this drawback, we prepare three-dimensional porous interfaces by pre-oxidizing the Cf/C composite. Results show that circular gaps are formed between the carbon fibers and the pyrolyzed carbon after pre-oxidization at 600 °C in air. Fster braze penetration in the Cf/C composite is achieved, and the heat-transfer area across the interface is dramatically increased. The room-temperature thermal conductivity of the joints reaches a maximum value of 146 W·m−1·K−1 at a pre-oxidation time of 2 min; this value is 30 % higher than that obtained without treatment. The enhancement in thermal conductivity is mainly attributed to the increased contact area at the interface between the brazing seam and the Cf/C matrix, which provides more channels for heat transfer. This method of significantly improving the thermal conductivity is an important guide for the thermal management of thermonuclear reactors.

Morphological and mechanical evolution of α-Al2O3 reinforced Mo[sbnd]Cu alloy obtained by planetary ball milling

MoCu alloys were fabricated by the mechanical alloying method and consolidated by cold and hot pressing at 950 °C with the addition of ceramic α-Al2O3 (1–2.5 wt%). XRD was used to define the crystallinity and lattice defects of the mixed powder, milled powders, and hot-pressed samples after mechanical alloying experiments. The crystallite size of Mo and Cu significantly decreased after the milling process and the homogeneous phase distribution was found in the hot-pressed specimen, however, large agglomerates of Mo and α-Al2O3 particles were found in the mixed specimens. The lattice parameter and lattice strain values indicated the existence of a finer Cu fraction positioned on the grain boundaries of Cu. Based on the SEM-EBSD analysis, the isotropic crystallographic texture was found in all samples. The hardness (265–266 HB) and yield strength (849–878 MPa) were significantly increased in the bulk samples due to the effect of milling and relative density still reached 95 %. The hardness and yield strength were improved in the milled and mixed samples by increasing the α-Al2O3 content, however, formability was decreased equally.

Amorphous interlayer assisted ductility of Mo-Cu alloy

Generally, binary immiscible alloys have poor plasticity due to weak interfacial bonding. In this study, an amorphous interlayer was introduced between Mo and Cu phases in Mo-Cu alloys by using the high-temperature infiltration method. With the increase of infiltrated temperature from 1300 °C to 1450 °C, the thickness of the amorphous interlayer wad increased from 2 nm to 13 nm. The formation process, thermodynamic driving force, stability of the amorphous interlayer in Mo-Cu alloy, and its contribution to mechanical properties were systematically investigated. By using the “macroscopic atom approach” Miedema's model, the thermodynamic driving force and stability of the amorphous interlayer were proved. It was found that the thickening of the amorphous interlayer can significantly improve the interfacial bonding, thus leading to an increase in the tensile strength of the Mo-Cu alloy from 520 to 600 MPa and failure strain from 0.15 to 0.31 The deformation behavior of the Mo-Cu alloy shows that the amorphous interlayer can effectively absorb interfacial dislocations during deformation, and relieve the stress concentration at the interface by crystallization, thus delaying the initiation and propagation of cracks at phase boundaries, which broke through the limitation of the trade-off between strength and plasticity of such Mo-Cu immiscible materials.

Improving the mechanical properties and coefficient of thermal expansion of molybdenum-reinforced copper using powder metallurgy

This paper presents an experimental study of Cu-Mo alloys prepared by powder metallurgy (PM) method. Also, improving the dispersion and wettability of Mo in the Cu matrix was aimed. Mo particles were added by 0.24, 0.48, 0.73 and 0.97% volume fraction to Cu powder. The mixture was mechanically milled by planetary ball mill at a rotational speed of 140 rpm for 24 h under hydrogen atmosphere, with milling ball size of ∼25 times the size of the metal powders. Liquid acetone was utilized as a process control agent (PCA). Paraffin wax (0.5 wt%) was used to decrease the friction with die during the compaction process. The mixture of the blended powder was compacted at ambient temperature under three different pressures (400, 600 and 800 MPa) and then sintered in a vacuum furnace at 1000 °C for 1 h by a heating rate of 5 °C min−1. The microstructure examination showed a homogeneous dispersion of Mo particles within the Cu matrix with no evidence of new phases formation during the sintering process. Also, the relative density of samples has been increased by increasing both of Mo content and the compaction pressure. The results revealed that the compaction pressure of 600 MPa was the most suitable pressure as it gave the highest densification. Cu—0.97% volume fraction Mo alloy samples exhibited finer Mo particles with a homogenous distribution in the Cu matrix and well bonding with the Cu particles. The microhardness was increased gradually by increasing Mo wt%, while the compressive strength was decreased by increasing the Mo contents. Both the electrical and thermal conductivities were decreased gradually by the addition of Mo. While the coefficient of thermal expansion (CTE) was decreased by Mo addition.

The effect of ball to powder ratio on the processing of a novel Mo-Cu-Al2O3 composite

In the present article a 45Mo-45Cu-10Al2O3 (wt%) nano-composite was produced by mechanical alloying, shaped by cold pressing then by hot pressing at 950 °C. Our aim was to investigate the effect of different ball to powder ratio (BPR) on the particle size and shape, as well as on the material composition. Investigations were done with XRD, SEM and for hot pressed specimens Brinell hardness measurement. Lower BPR resulted in nano-sized crystallites in the powder, a homogenous phase distribution and higher BPR resulted in even smaller crystallite sizes, but with ZrO2 contamination from the milling equipment. The milling resulted in two separate fractions in the metallic phases separated by crystallite size, strain and lattice parameter. After hot pressing, the lower BPR powders developed a homogeneous, evenly distributed microstructure. Cu recrystallized during hot pressing, but still remained nanocrystalline, the crystallite size of Mo and α-Al2O3 decreased even more due to crystallite deformation and in the case of Mo, the lattice strain values indicates that recovery had also happened. The heating eliminated the crystal defects at highly strained areas and the subsequent cooling evened out the stresses in the respective metallic phases. The inner grain structure was revealed by etching, showing that α-Al2O3 particles congregated only at the Mo grain boundaries, but penetrated the Cu grains. The lattice strain values combined with the BSE images reveal that the Cu is the main matrix of the α-Al2O3 particles. The results indicate that the α-Al2O3 particles induced Particle Stimulated Nucleation (PSN) in the Cu explaining its moderate crystallite size increase. The hot pressed samples of higher BPR had higher ceramic (ZrO2 and α-Al2O3) content, resulting in higher hardness, but lower relative density (92.4%), compared to the samples of lower BPR, which reached 97.2% relative density and hardness still significantly higher than MoCu alloys.

Study on the microwave sintering of the novel Mo–W–Cu alloys

In this study, we fabricated a new type of Mo–W–Cu alloys by microwave sintering at a low temperature (1000 °C) in a short time (5 min) and characterized the phases, microstructures, and properties of the alloys. Through calculating the skin depth, it was proved that the microwave field enabled complete penetration of radiation to Mo, W, and Cu particles, thus effectively promoting the diffusion and solid solution among Mo, W, and Cu. XRD and TEM results showed that Mo-W-Cu alloys contained three new phases besides Mo, W, Cu phases, i.e., Mo-W ordered phase, Mo-Cu solid solution, and Cu0.4W0.6 intermetallic compound. It was also found that Mo–W–Cu alloys exhibited better densification and comprehensive properties than Mo-Cu alloys. The number and size of the sintering necks varied with the W content from 10 to 50 wt% among which the optimal microstructure and properties were obtained at 30 wt% W. This study could provide useful guidelines for further research of the densification and properties of microwave sintered Mo-W-Cu alloys.

Synthesis of Mo-Cu Nanoalloys and Computer Aided Thermal Analysis of Mo-Cu Nanoalloys Based Heat Sink

Mo-Cu alloys are used as heat sinks, microwave absorbers in microelectronic devices and as electric contacts in circuit breakers. Mo-Cu nanoalloys with average sizes below 200 nm were prepared using molybdenum powder and copper nitrate. Compositional characterization of Mo-Cu alloys was carried out using portable XRF. The developed material i.e. Mo-Cu is used as heat sink application in which the heat sink is modeled and thermally analyzed for evaluation of heat flux. The heat flux obtained was compared with heat sink made of aluminum. It was observed that the Mo-Cu heat sink exhibited superiority in withstanding higher temperature whereas, heat sink designed from aluminum was limited with their parameter which is thermal conductivity.

3-D phase-field simulations of self-organized composite morphologies in physical vapor deposited phase-separating binary alloys

We use 3D phase-field simulations to investigate the role of deposition rates and atomic mobilities on morphological self-structuring in phase-separating, vapor-deposited alloys. Our numerical simulations predict the three distinct nanocomposite morphologies: vertical composition modulations (VCMs), lateral composition modulations (LCMs), and random composition modulations. We also observed a transitional region between VCM and LCM that exhibits the coexistence of features drawn from both morphologies. We compare these results with experiments carried out on co-deposited Cu-Mo alloys and find good agreement between the two.

Effects of Ball Milling Processing Conditions and Alloy Components on the Synthesis of Cu-Nb and Cu-Mo Alloys.

The effects of processing parameters in ball milling and the different behaviors of Cu-Nb and Cu-Mo alloys during milling were investigated. High powder yields can be obtained by changing the BPR value and ball size distribution and no clear dependence of BPR value on powder yield can be found from the experiment results. The addition of oxygen can largely reduce the effect of excessive cold welding during ball milling. A “two-step” ball milling method was introduced to evaluate the different evolution processes and morphologies in different alloys. With 8 h pre-milling, this method considerably benefits the oxidation process of Mo and shows its promising potential in the synthesis of immiscible alloys. Based on the experiment results and analysis, we suggest that the different behaviors of Cu-Nb and Cu-Mo alloys are related to the shear modules and different tendencies to be oxidized.

Thermodynamic analysis of Fe contamination in Cu-Mo alloys processed by mechanical alloying

ABSTRACTThis work aims to verify if Fe atoms coming from balls and jars enter into solid solution of Cu-Mo powders during mechanical alloying. The powders were milled and its structure and composition were characterised by scanning and transmission electron microscopy, and X-ray diffraction. Gibbs free of mixing values for Cu-Mo-Fe system were calculated using the Miedema’s model and showed that Cu-rich corner exhibit smallest energy values (<10 kJ mol−1). The observed coherency relation Cu(111) || Mo(101) || Fe(101) confirmed formation of solid solution. Fe atoms have entered in solid solution with Cu and Mo and do not remain as particles of second phase.

High thermal coarsening resistance of irradiation-induced nanoprecipitates in Cu-Mo-Si alloys

Irradiation by 1.8 MeV Kr ions at room temperature (RT) was employed to induce nanoprecipitation in two Cu-Mo-Si ternary alloys, Cu96Mo1Si3 and Cu90Mo3.5Si6.5. The nature and the stability of these precipitates during high temperature annealing and irradiation were studied using X-ray diffraction and transmission electron microscopy. In Cu90Mo3.5Si6.5, Kr irradiation at RT resulted in the formation of a high number density (>1023 m−3) of Mo-Si rich nanoprecipitates, ∼3 nm in size, the formation of which was attributed to Mo-Si interactions during the thermal spike phase of displacement cascades. The size of these irradiation-induced Mo-Si precipitates remained unchanged after annealing at 750 °C for 1hr. This near absence of thermal coarsening contrasted with a significant thermal coarsening of the more Mo-rich precipitates formed by direct annealing in that same ternary alloy, and with the even larger coarsening of pure Mo precipitates formed by RT irradiation in binary Cu-Mo alloys. During high temperature irradiation, precipitation is also observed, and some precipitates were significantly enriched in Mo. As for thermal annealing, those precipitates displayed increased coarsening. The remarkable thermal coarsening resistance of RT irradiation-induced Mo-Si precipitates is attributed to the suppression of Mo solubility in a Cu matrix containing Si-rich precipitates, and to the narrow precipitates size distribution generated by RT irradiation. This former point was quantified using thermodynamic calculations with the CALPHAD method.

Preparation and Evaluation of Electroplated Cu-Mo Alloy Films

Recently heat radiation was important issue by downsizing and integrating electronic devices. However, coefficient of thermal expansion of heat radiation material was different from that of semiconductor. The heat radiation materials with high heat conduction and low coefficient of thermal expansion were strongly requested. A copper-molybdenum alloy was one of the most promising candidates for the heat radiation material with low coefficient of thermal expansion. The copper-molybdenum alloy films were electroplated by using pulse plating method. Platinum plate and nickel plate were used as counter electrode and substrate, respectively. Nickel substrates were activated by 10% H2SO4 at room temperature for 1 minute after NaOH alkaline degreasing at 60℃ for 10 minutes. Thickness of Cu-Mo alloy films was adjusted approximately 3µm. The bath conditions of Cu-Mo electroplating using Na2MoO4 2H2O and CuSO­­­­­­­­4 5H2O.Trisodium citrate dehydrate (C6H5O7Na3 2H2O) was used as complexing agent. The solution pH was adjust at 9.0 in order to avoid generation of insoluble molybdate in acid solution.The surface morphology and the crystal structure of Cu-Mo alloys was observed by scanning electron microscope (SEM: KEYENCE VE-8800) and X-ray diffraction (XRD: RIGAKU RINT2200) .Table1 Effect of Mo content on Cu(111) plane peak position intensity of Cu-Mo alloy films plated from baths with different temperature. Temperature ( oC)Mo content (at%)Cu(111) peak position (o)Cu(111) peak intensity (cps)Half-value width of Cu(111) peak (o)Grain size (nm)2.01.9343.395821.060.10820.015.043.016041.350.14930.018.343.276021.230.11440.012.243.2512780.370.38750.06.743.3219260.4030.32360.00.743.2215760.5840.260 Figure 1 showed effect of bath temperature on surface morphology (a), observed by scanning electron microscopy (SEM), and X-ray diffraction (XRD) patterns (b) of the Cu-Mo alloy films. Grain size was decreased with increasing bath temperature for the region from 2.0 oC to 30 oC. Surface roughness was increased with increasing bath temperature for the region from 30 oC to 50 oC. However, grain size of the film plated at 60oC was smaller than that at 50oC and surface roughness of the film plated at 60oC was also smaller than that at 50oC. Molybdenium content of the films plated at 2.0oC was almost the same as that plated at 60oC. The surface morphology was quite different. The grain size of the film plated at 60oC was much smaller than that plated at 2.0oC, however from the XRD measurement, as shown in Table1, the grain size of the film plated at 60oC was larger than that plated at 2.0oC.Moreover, the Copper (111) plain peak intensity of the film plated at 60oC was much stronger than that plated at 2.0oC as shown in Fig.1 and Table 1.The copper plain peak position of the film plated at 30oC was 43.27o, Mo content was 18.3 at%. On the other hands, the copper plain peak position of the film plated at 20oC was 43.01o, Mo content was 15.0 at%. Since the molybdenum content of the film plated at 30oC was higher than plated at 20oC, Cu (111) plane peak position was shifted to higher angle side. Co-deposition Mo was formed solid solution with Cu and was widened interplanar spacing of Cu (111). The films plated at 20oC and 30oC showed low degree crystallization, they show high Mo content, 15.0at and 18.3at%, respectively. The co-deposited Mo deteriorated degree of crystallization. The peak intensities of Cu (111) plane were increased with increasing bath temperature for the region from 30oC to 50oC by decreasing Mo content from 18.3 to 6.7at%. However, molybdenum content was decreased with increasing bath temperature, from 18.3 to 0.7at%, for the region from 30oC to 60oC. The peak position of Cu (111) plane was almost constant. Therefore segregation of Mo was enhanced by decreasing bath temperature. Figure 1

Comparisons on Arc Behavior and Contact Performance between Cu and Cu-Mo Alloys in a Bridge-Type Contact System

Comparisons on Arc Behavior and Contact Performance between Cu and Cu-Mo Alloys in a Bridge-Type Contact System

Codeposition of Copper and Molybdenum by Electroplating

Electronic devices are desired to be larger integration, smaller size, higher speed and higher power, resulting in larger thermal generation, recently. Thermal generation from electronic devices such as a light-emitting-diode degrades reliability and lifetime, also causes thermo-mechanical stress, leading to distorting and breaking chips or packages. The thermo-mechanical stress is due to the difference of thermal expansion coefficient between chips and packages. Reduction of elevated temperature and thermo-mechanical stress is one of important issues for electronic devices. To overcome this phenomenon, it is required that coefficient of thermal expansion and thermal conductivity of heat-sink materials contacted to chips are close to those of semiconductor chips such as silicon or GaAs. A Cu-Mo alloy has high thermal conductivity, low coefficient of thermal expansion and high mechanical strength. The typical thermal conductivity of CuMo alloys is approximately 210 W/(m K), which is similar order to that of silicon (151 W/(m K)) or GaAs (400 W/(m K)). Thus, a Cu-Mo alloy is one of candidates for heat sink materials in electronic devices. A Cu-Mo alloy has been reported as material of a heat spreader or a heat sink. 1‐7 A Cu-Mo alloy has been adopted as subcarriers, and been attached microwave monolithic integrated circuits, 2 moreover, has been used as heat spreader in insulated gate bipolar transistors. 3,5

Structural study by X-ray profile analysis and thermodynamics properties of Cu-Cr and Cu-Mo alloys processed by mechanical alloying

Structural study by X-ray profile analysis and thermodynamics properties of Cu-Cr and Cu-Mo alloys processed by mechanical alloying

Powder Metallurgy Research and Development Activities at USTB

University of Science and Technology Beijing (USTB) is one of the key universities that are directly under the guidance of China Ministry of Education. Powder metallurgy activities have been carried out at USTB for about 50 years. Beijing Key Laboratory for Advanced Powder Metallurgy and Particulate Materials, which was founded on the base of Department of Powder Metallurgy at USTB, is a comprehensive base for PM education, research and development in China. In this paper, some of the current research activities and achievements in this laboratory are introduced, including ultra-fine grained cemented carbides made from nanometer powders, W-Cu and Mo-Cu alloys for electronic packages, SHS process and its applications, warm compaction, and powder injection molding.

Cu-Mo Alloys Obtained by Mechanical Alloying

Cu-Mo Alloys Obtained by Mechanical Alloying

Shape distortion in liquid-phase-sintered tungsten heavy alloys

Shape retention during liquid phase sintering is a major concern at high liquid contents, or large density differences between the solid and the liquid phases. This study demonstrates the role of microstructural parameters in controlling the bulk dimensional changes that occur during liquid phase sintering of tungsten heavy alloys (WHAs). Tungsten-nickel-copper alloys containing 80 wt pct tungsten, the balance containing Ni and Cu in the ratio 6:4, 7:3, or 8:2, were sintered at temperatures between 1400 °C and 1500 °C. Compact distortion was quantified using a coordinate measuring machine and related to the microstructural parameters, such as solid volume fraction, grain size, dihedral angle, grain continguity, and connectivity. Supplementary experiments were performed on W-Ni, W-Cu, and Mo-Cu alloys to compare the role of microstructural parameters in controlling distortion. A low solid solubility and a small grain size coupled with a high dihedral angle and connectivity restrict distortion. Based on the experimental observations and stereological relations, the critical solid content required to maintain structural rigidity is related to specific combinations of dihedral angle and grain connectivity.

Mixing and Demixing of Cu-Mo

AbstractIon beam mixing of Cu/Mo multilayer samples and demixing of Cu-Mo alloy samples were examined as functions of temperature and ion mass. Even at liquid nitrogen temperature, the mixing of one component in other was very small under 1.0 MeV Kr irradiation. The maximum solubility was about 10%. Irradiation of homogeneous Cu-Mo alloys under the same conditions, moreover, led to phase separation. These conclusions were deduced from bulk X-ray diffraction measurements and corroborated by EXAFS examination. The maximum solubility obtained by irradiating multilayer samples occurred at about 600 K. At lower or higher temperature, the solubility of Cu in Mo-rich phase was lower. A model based on the ballistic difflusion explains these results.