查看更多>>摘要：Cubic boron nitride (cBN) (Al)-Al2O3 composites were synthesized by Chinese multi-anvil high pressure apparatus (CHPA) sintering at 5.0 GPa and 1200-1500 & nbsp;C using Al-coated cBN (cBN (Al)) and Al2O3 powders. The effects of Al coating, phase composition, densification, Vickers hardness and thermogravimetry of the composites were investigated. Al coating on cBN powder activated the surface of cBN in the composites and reacted with cBN to produce AlN under high pressure and high temperature (HPHT) environment, which helped to promote the bonding strength of cBN and Al2O3. The hardness of cBN (Al) + 15 vol% Al2O3 is 29.7 GPa when sintered at 5.0 GPa and 1350 & nbsp;C. Compared to cBN-Al2O3 composites, the hardness of cBN (Al)-Al2O3 composites increased by 37.5%. AlN, the reaction product of cBN with Al under HPHT environments, acts as a bridge phase and joins the two phases of cBN and Al2O3 in the form of chemical bonds. This is the intrinsic mechanism of hardness improvement of cBN (Al)-Al2O3 composites.
查看更多>>摘要：Tungsten carbide hard metal alloy with 6% by weight cobalt was studied before and after irradiation at different fluencies with 167 (MeVXe)-Xe-132 ions. Raman spectroscopy, X-ray diffraction, neutron diffraction and positron lifetime spectroscopy were employed in order to assess the microstructural evolution in the material upon irradiation fluence increase. Analysis of the Raman spectrum for the pristine, non-irradiated material unveils that the surface is composed of a graphite-like phase and highly oxidized tungsten atoms spread in the carbon matrix. All characteristic peaks of tungsten carbide (WC) and possible cobalt phases are either missing or strongly overlapped in all Raman spectra. Bonding between tungsten and oxygen atoms broke upon irradiation and total deoxidation of the surface is detected for the two highest fluencies investigated at 5 x 10(13) ions/cm(2) and 3,83 x 10(14 )ions/cm(2). Increasing the irradiation dose causes amorphization of the carbon phase on the surface accompanied by "up and down " trend of change in carbon cluster size. The Raman spectra analysis also unveils, that molecular nitrogen (N-2) from the atmosphere penetrates the carbon matrix upon irradiation. The results from the X-ray and neutron diffraction reveal that the main phase in the material is delta-WC and also give information about changes of the lattice parameters with increasing fluence. Reorganization of the induced point defects to dislocation defects as a function of the irradiation dose is discussed, but no phase transition of the main delta-WC phase is detected. Steady increase of compressive internal stress with increasing irradiation dose is noted by XRD. The tendency is not monotonic and the stress leans towards saturation at the highest fluence, with the highest value of-5.26 GPa. The Positron lifetime spectroscopy measurements show the presence of short lifetime component ranging from 170 ps to 190 ps, interpreted as small vacancy clusters. The intensities of the different positron lifetime components vary with the irradiation dose non-monotonically.
查看更多>>摘要：To reduce the decarburization of WC, the core-shell WC-16Cr(3)C(2)-10Co4Ni-La2O3 (named as WC-Cr3C2-CoNiLa in following) powder was prepared through second agglomeration and spray granulation process and deposited using high velocity oxygen fuel (HVOF) spraying. Microstructure and phase constitutions of the deposited coating were characterized using scanning electronic microscopy (SEM) with energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. Microhardness, elastic modulus, and fracture toughness of the coating were tested by indentation method. Wear properties of the coating under different applied loads were evaluated by two body dry sliding wear using a pin-on-disc tester. Experimental results showed that the HVOF sprayed WC-Cr3C2-CoNiLa coating was mainly consisted of WC, Cr3C2, Co, Ni phases and a little of Cr2O3 without any WC decarburized phases including W2C, M6C and M12C). Most of WC carbide in the coating presented a round outline with the average particle size of 0.54 +/- 0.35 mu m and average crystal sizes 401 +/- 91.41 angstrom. in different crystal orientation index. The coating presented dense microstructure with the porosity about 1.16 +/- 0.39%, and some lamella features with well bonded interfaces of carbide particles/binder phase, inter-splats and coating/substrate. Microhardness, elastic modulus, fracture toughness and wear rate of the coatings were 12.57 +/- 0.52 Hv0.3, 153.91 +/- 31.66 GPa, 5.31 +/- 0.51 MPa.m(1/2) and 6.67*10(-3)-11.11*10(-3) mg/(Nm) when the applied load increased form 5 N to 15 N, respectively. The abrasive wear of the coating occurred mainly in the form of gouging and plastic deformation as well as peeling off carbide particles.
查看更多>>摘要：Powder metallurgy approach was used to produce fine-grain tungsten heavy alloys (WHAs), and the effect of Mo addition on the microstructures and mechanical properties of the alloy was discussed. The W-Mo-Ni-Fe ultrafine composite powders were prepared via method consisting of steps of carbothermic pre-reduction and subsequent deep hydrogen reduction. The sintered compacts of these W-Mo-Ni-Fe composite powders reached virtually full densification after sintering at 1500 ?C for 2 h. It was discovered that the W grain size of WHAs reduced due to the Mo addition (0, 2.5, 5, 10 wt%). Tensile test results showed that the alloy with 5 wt% Mo exhibited the maximum ultimate tensile strength and elongation, which has a significant relationship with finer W grain size, lower W-W contiguity and higher volume fraction of the gamma-(Ni, Fe) matrix phase. It was also concluded that the major fracture characteristic of WHAs were transformed from W-W decohesion to W-matrix interface separation with increasing the addition amount of Mo.
查看更多>>摘要：In this research work, the first-principles calculation was used to predict the WC/Cu interfacial properties, and the prediction results were verified by experiments. The surface properties of different low-index surface models of WC(0001), WC(1010), WC(1120) and Cu (111), Cu (100), Cu (110) were firstly clarified. And then the nine low-index WC/Cu interface models with different configurations were constructed. The adhesive work, interfacial energy and electronic structure of WC/Cu interface were studied to predict the interfacial bonding properties. The results showed that W-terminated WC(0001)/Cu(111) interface with the stacking site of FCC has the highest adhesive work (4.270J/m2) and lowest interfacial energy (0.481-0.815J/m2) due to the strong metallic bonds and covalent bonds interactions between W and Cu atoms at the interface, which indicated that the W-terminated WC(0001)/Cu(111) interface is more likely to exist in reality. The high-resolution transmission electron microscope (HRTEM) experimental results have showed that the WC/Cu interface has the crystallographic orientation relationship of WC[1120]//Cu[101], WC(0001)//Cu(111). The WC(0001)/Cu(111) interface displays a plane-to-plane matching with semi-coherent atomic correspondence, which are well consistent with the first-principles prediction results.
dos Santos, Alessandra Agna A.Guimaraes, Renan da Silvade Carvalho, Cassio S.Soffner, Max Erik...
9页
查看更多>>摘要：The most advanced alternative to replace cobalt in cemented carbides is alloys based on the Fe-Ni-Co system due to their similar or superior properties to conventional Co-binder. However, recently, successful cermet alloys with Fe-Ni-Nb as a binder have been reported. In this work, cemented carbides NbC-10% wt Fe-Ni-Nb were prepared by solid state pulsed electrical current sintering (PECS), also known as spark plasma sintering (SPS), for 5 min, 40 MPa at temperatures 1280 degrees C, 1300 degrees C and 1350 degrees C. The samples produced were investigated focusing on their structure, mechanical and thermal properties. All samples showed an increase in NbC crystallite size and n-phase formation. The processed NbC-FeNiNb cermet presented good densification and hardness of approximately 1726 HV30, fracture toughness 12.5 +/- 0.1 MPa.m1/2, Young's modulus 385 +/- 4 GPa, which is shown as a viable alternative composite in applications cemented carbide such as cutting tools. However, these cermets could have even better properties, eliminating the intermetallic phase present in the matrix and decreasing its particle size. TG and DSC analysis confirmed the formation of a liquid phase and more carbides contributing to the mechanical properties of the composite. The thermal properties showed that the thermal diffusivity and thermal conductivity for NbC-FeNiNb was lower than for WC-Co carbide.
查看更多>>摘要：Restraining diamond graphitization is still the potential problem for brazed diamond tools with Ni-Cr filler alloys. Herein, we systematically investigate the interfacial bonding and mechanical performance of brazed diamond tools with Cu-doping Ni-Cr filler alloys through multi-scale atomistic simulations and experiments. First-principles calculations show that the Cu-doping not only inhibits the structural damage of diamond, but also enhances the metallurgical bonding between diamond and filler alloys. The tensile simulations of Ni-Cr-Cu/ diamond interface further verify the strengthening effects of Cu-doping since these bonds of C-C within diamond and Ni-Cr-C at interface can withstand greater tensile strains. Combined with molecular dynamics simulations, Cu-doping effectively weaken the graphitization of diamond, which is confirmed through experimental Raman spectroscopy detection. More importantly, the brazed diamond tools by Ni-Cr filler doped with 40 wt% Cu alloy exhibit excellent mechanical grinding performance. These results shed a new light on improving the mechanical properties of brazed diamond tools.
查看更多>>摘要：ZTA is an innovative ceramic composite for advanced industrial applications because of its superior mechanical properties compared to both pure Al2O3 and ZrO2. Therefore, it was subjected to extensive study since 1970s. The last review by Wang and Stevens (1989) focused on the development of ZTA ceramics through controlling powder preparation and densification processes. The current review verified the effects of adding various additives into ZTA ceramics utilising several sintering techniques and preparation routes to further enhance their mechanical properties through governing their microstructure pattern. It shows that the porosity, number and total quantity of additives, the reaction of additives with ZTA ingredients, grains sizes, and the number of secondary phases are important parameters affecting the mechanical properties of ZTA. This review also reported the most recent progress in the enhancement of mechanical properties of ZTA as an alternative to other costly related advanced materials industries and suggested a few approaches to accomplish this objective.
查看更多>>摘要：This paper presents the results of the investigation of the microstructure and properties of copper-tungsten coatings with different compositions on aluminum alloy substrates. Coatings were obtained by cold spray method using powder mixtures as feedstock. The effect of the powder mixture composition on the deposition efficiency and the tungsten content in the coating have been studied. X-ray diffraction analysis was used to investigate the phase composition and to reveal the peculiarities of changes in the crystalline structure of copper and tungsten particles after cold spraying in relation to the coating composition. Using the method of instrumental indentation on cross-sections of the coatings mechanical properties were measured. It was shown that increasing of tungsten content in the coatings contributes to increasing the microhardness and Young's modulus of the coatings. The mapping images showed that all coatings were characterized by non-uniformity of mechanical properties over the cross-section. The bonding strength of coatings significantly increases with increasing tungsten content in the feedstock. Cu-W coatings are characterized by lower specific wear rate values and higher coefficients of friction under dry sliding wear conditions in a ball-on-flat mode compared to pure copper coating.
查看更多>>摘要：High-pressure torsion (HPT)processing with floating cavity was carried out under the applied pressure of 1.5 GPa with the revolution from 5 to 20 turns at the temperature of 300 degrees C, and the W-Cu gradient material with noble bonding interface and significant grain refinement was successfully obtained. The microstructure evolution and atomic diffusion around the bonding interface were analyzed by electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) in a field emission scanning electron microscope (SEM). The mechanism of large shear strain on the microstructure evolution and diffusion ability of tungsten and copper at the interface was investigated. The results show that HPT processing with floating cavity can effectively refine microstructure of tungsten and copper to submicron. After 5 turns of HPT deformation, the grain size of copper was significantly refined to 0.59 mu m but experiences slight increases to 0.8 mu m with the additional revolution number to 20 turns, and the ultrafine equiaxed grains with relatively straight grain boundaries and few dislocations within grains were formed under the continuous dynamic recrystallization mechanism. However, the microstructure of tungsten was continuously refined within 20 turns of HPT processing due to the accumulation shear deformation, and a lamellar microstructure was formed along the W-Cu bonding interface with a gradient distribution in the width of banded grains from 0.06 mu m at the interface to 0.33 mu m towards the tungsten matrix. In addition, with the increase of torsion strain, the diffusion lengths of tungsten and copper gradually increasing to 1.6 mu m and 6.2 mu m, the interdiffusion coefficient of tungsten in copper remained basically constant, while the value of copper in tungsten increases continuously. The high density of defects and ultrafine grains with high angle boundaries introduced by large shear deformation of 20 turns of HPT processing play roles in the rapid diffusion paths to accelerate the atom diffusion and the interdiffusion coefficient of tungsten and copper is enhanced by 0.48- 1.79x 108 times compared to the lattice diffusion.
NSTL
Elsevier