Steinlechner, R.Calderon, R. de OroKoch, T.Linhardt, P....
18页
查看更多>>摘要：The manuscript presents a systematic study on three groups of Ni-based cemented carbides (WC-20 wt% Ni, WC-20 wt% Nil5Cr and WC-20 wt% Ni11Cr6Mo) based on thermodynamic calculations and experimental studies. Samples were prepared with different gross carbon contents (carbon activities) with the aim to provide a comprehensive overview on: constitution and phase formation, solubility of elements in the binder phase, binder and composite hardness, as well as their corrosion behaviour. A WC-20 wt% Co8Cr was used as standard binder system for comparison. The results show that the amount of alloying elements that can be dissolved in the binder phase is significantly higher in the Ni binder as compared to the Co binder (e.g., the solubility of W in WC-Ni is about double of that observed in conventional WC-Co). The degree of alloying is primarily affected by the carbon content. The lower the gross carbon content within the processing window, the higher is the degree of binder alloying. In WC-Ni, up to 12 at% W is observed in solution in low carbon alloys, as compared to 4 at% W in high carbon grades. Additions of Cr are limited to 9-11 at% Cr, depending on the gross carbon content. When exceeding this value, Cr3C2 is formed in high carbon Ni alloys. The solubility of Mo in WC-NiCrMo cemented carbides is limited to about 2 at%, at higher additions a carbide is formed, most likely (W,Mo)C. The high hardness values observed in NiCr and NiCrMo alloys when compared to plain Ni alloys can be attributed to the effect of Cr and Mo as WC grain growth inhibitors, and not to a significant enhancement of the intrinsic binder hardness. In contrast, our standard Co grade demonstrated a significantly higher binder and composite hardness than all of the nickel variants studied. Finally, high-alloyed materials (low carbon NiCr- and NiCrMo alloys) did present a superior corrosion resistance compared to the CoCr grade even in the most severe corrosion environments. Higher degree of alloying (i.e., higher amounts of Cr, W, and Mo present in solid solution in the binder) is indicative of superior corrosion behaviour due to the nature of the protective layers formed under corrosive environments.
查看更多>>摘要：Cemented carbides is widely used in industrial fields, but it is difficult to meet the needs of the evolving modern industry due to the shortage of cobalt resources and the difficulty to balance hardness and toughness. In order to solve this problem, a high-entropy alloys (HEA) as the novel binder were used to fabricate WC-10Co(x)FeNiCrCu (x = 1, 1.5, 2, 2.5) cemented carbides. CoxFeNiCrCu (x = 1, 1.5, 2, 2.5) HEA powders were prepared by mechanically alloying and powder mixes of WC and the HEA were obtained by high energy ball-milling. Spark plasma sintering (SPS) was used to fabricate the WC-10HEA cemented carbides. Effects of Co content in the HEA binder and sintering temperature (1300 degrees C, 1350 degrees C, 1400 degrees C, 1450 degrees C) on the microstructure and properties of the resultant WC-10HEA cemented carbides were investigated. After SPS sintering at 1400 degrees C and 30 MPa for 8 min, the WC-10Co(x)FeNiCrCu cemented carbides had finer grain size and better mechanical properties then the conventional cemented carbides with cobalt as binder. The cemented carbides with Co1.5FeNiCrCu as binder had average WC grain size about 398(+/- 67.94) nm, and Vickers hardness up to 2078.2 (+/- 40.35) MPa and the fracture toughness was 11.636(+/- 0.1) MPa.m(1/2). The present work indicates that HEA has the potential to replace conventional Co as a new binder, because of its finer grain and high hardness.
Paul, BhaskarKishor, JugalKarthik, A.Murthy, Tammana S. R. C....
8页
查看更多>>摘要：Friction, wear and mechanical properties of the liquid phase sintered W-2Ni-1Fe (wt%) alloy were investigated. Tribological tests were carried out at different loads, frequencies and sliding distances under reciprocative sliding condition, against tungsten carbide (WC-Co) counter body. Co-efficient of friction (COF), wear volume and specific wear rate were determined. The dominant operative wear mechanisms were identified in different testing conditions. Abrasive wear and tribo-chemical wear mechanisms were found to be the dominant wear mechanisms. Room temperature strain rate sensitivity was determined by conducting jump test in tensile mode. The alloy showed low strain rate sensitivity with significant strain hardening. High resolution nanoindention mapping was carried out to establish structure property correlations at the micro-meter length scale. The hardness and elastic modulus maps were generated to determine the hardness and elastic modulus of the constituent phases of W and of gamma-Ni matrix. The maps were found to correlate well with the actual microstructure obtained from opticaland electron microscopy.
查看更多>>摘要：The present investigation deals with the synthesis and characterization of oxide dispersed strengthened (ODS) alloys based on W79Ni10Nb5Mo5 (in weight %) with 1.0 wt% of nano Y2O3 (alloy A), TiO2 (alloy B) and ZrO2 (alloy C) respectively by mechanical alloying for 20 h using Ball to Powder weight ratios (BPR) of 10:1 and 5:1. X-ray Diffraction study reveals that the mechanically alloyed alloy A with 10:1 BPR possesses minimum crystallite size (11.15 nm). A high-resolution Transmission Electron Microscopy study shows that oxide particles are dispersed at the particle interface and matrix. HRTEM study also reveals different orientation of lattice fringes of the oxide with respect to the matrix with a positive and negative lattice misfit is evaluated in the alloys milled with 10:1 BPR.
Voronova, L. M.Chashchukhina, T., IGapontseva, T. M.Patselov, A. M....
10页
查看更多>>摘要：The effect of the initial orientation on structure development upon severe plastic deformation performed by high pressure torsion at room temperature has been investigated on molybdenum single crystals of two orientations (110) and (113). The initial orientation of molybdenum has been found to affect its deformability, texture, and the size of structural elements significantly only at the initial stages of deformation. Single crystal with the (113) orientation is more stable to deformation. Its fragmentation starts at a higher true strain than the fragmentation of the single crystal with the (110) orientation. An increase in the true strain above 6 completely neutralizes the effect of the initial orientation on the structure development.
查看更多>>摘要：Refractory high-entropy alloys (RHEAs) usually exhibited good mechanical properties at high temperatures. Unfortunately, the very poor high-temperature oxidation resistance was still greatly limited their practical application space. In this work, the effect of the reactive element (RE) Y on the high temperature oxidation resistance of CrMoTaTi RHEA was systematically investigated. It was found that the addition of Y could significantly improve the high-temperature oxidation resistance of CrMoTaTi RHEA. For the Y-bearing RHEAs, they greatly reduced the critical concentration of Cr required for the formation of Cr2O3 on the alloy surface, which was conducive to the rapid formation of Cr2O3 reacting with Ta2O5, resulting the generation of CrTaO4 with a relatively dense and continuous protective layer. The Y-bearing RHEAs exhibited good oxidation resistance even when the alloys were oxidized at 1000 degrees C for 100 h. This work proposed a positive role of the reactive elements and new insights to improve the high-temperature oxidation resistance of RHEAs.
查看更多>>摘要：Preparation of a ternary ReBx-Ti compound within a single magnetron target, forming a plasma surface sintering (PSS) conditions, were investigated. An ionized-neon pressure of 40 Pa induced sintering power pulses (E-i) with energies of up to 3.1 kJ, which resulted in a low-porosity rhenium boride (3.2%) structure within a solid titanium matrix (ReBx-Ti). The prepared targets showed promising resistance to high temperatures (5.45 mm(2)/s of thermal diffusivity), after the PSS process at a temperature above 2100 degrees C. These as-surface-sintered magnetron targets were further used in gas injection magnetron sputtering to obtain Re-B-Ti films characterized by an enhanced deposition rate (120 nm/min). Quantitative analysis of these films revealed that the B/Re ratio was in deficit in comparison to the stoichiometry of as-prepared cathode materials. A multiple-chemical-bond state showed the occurrence of Re-B, Ti-B, B-B, Ti-Ti, Ti-O, and B-O phases, of which TiB2 and ReB2 were dominant, forming therefore a glass-like structure. All gathered data indicated a maximum Vickers microhardness value (36.4 GPa), emphasizing the valuable mechanical response of the deposited Re-B-Ti films, as well as the retaining of their good self-passivation effect, attributed by the oxide phases.
查看更多>>摘要：Ni bonded (Nb,W,Ti)(C,N) solution cermets with overall compositions of NbC-(6-20)Ni-18WC-14 Ti(C0.7N0.3) (wt%) were prepared by pressureless vacuum sintering of compacted NbC, Ni, WC and Ti(C0.7N0.3) mixtures. The microstructure, phase constitution, room temperature mechanical properties were investigated and the phase composition in the cermets sintered at 1450 degrees C was simulated by thermodynamic modelling. The sintered cermets exhibited a microstructure of a cubic Ni alloy binder dispersed in the matrix of core-rim structured (Nb,W, Ti)(C,N) complete solid solution grains. The average ceramic grain size was in the range of 1.5-2.1 mu m and increased with increasing binder content and sintering temperature. The hardness decreased whereas the fracture toughness and flexural strength increased with increasing Ni content. For the cermets sintered at 1450 degrees C, the 6 wt% Ni cermet had a hardness of 1627 kg/mm(2), a toughness of 7.8 MPa.m(1/2) and a flexural strength of 1478 MPa. The toughness and strength were improved to 13.1 MPa.m(1/2 )and 2446 MPa in the cermet with 20 wt% Ni.
查看更多>>摘要：(Ti0.88W0.12)C solid-solution is characterized by the lowest formation energy and hence it can significantly affect the microstructure and properties of Ti(C,N)-based cermets. This research aims to explore the design principle for (Ti0.88W0.12)C addition amount, and the related strengthening mechanism. 28TiC(0.7)N(0.3)-35(Ti(0.88)Wa(0.12)) C-4.5TaC-4.5NbC-8Mo(2)C-10Ni-10Co (A) and 48TiC(0.7)N(0.3)-15(Ti0.88W0.12)C-4.5TaC-4.5NbC-8Mo(2)C-10Ni-10Co (B) were prepared. On considering the application market expansion, the effect of TiC0.7N0.3/(Ti0.88W0.12)C ratio on the microstructure, mechanical properties and corrosion resistance was investigated. The results show that the hard phase in the two cermets exhibits a preferred orientation of (111) plane. Compared with cermet A, cermet B is characterized by a more uniform microstructure, finer hard phase grains, and 1.23 times higher transverse rupture strength (TRS). Hardness, Palmqvist toughness and TRS of cermet B are 90.5HRA, 12.1 MPa m(1/2) and 2616 MPa, respectively. Hardness and toughness of cermet A are 0.4 HRA and 1.06 times higher than that of cermet B, respectively. The results of electrochemical corrosion experiments in H2SO4 (pH = 1) and NaOH (pH = 13) solutions show that cermet B exhibits better corrosion resistance. Both the cermets exhibit excellent resistance to NaOH solution corrosion. The strengthening mechanism driven by TiC0.7N0.3/(Ti0.88W0.12)C ratio is discussed.
查看更多>>摘要：The pure vanadium cold-rolled foils were sequentially annealed at elevated temperature, followed by measurements using positron annihilation and XRD techniques. It was found that in the recovery stage in the temperature range from 100 to 450 degrees C, a significant rearrangement occurs in the dislocation microstructure, which confirms the reduction of the first positron lifetime component. The recrystallization process was beginning at 650 degrees C and proceeds to 800 degrees C or more what is associated with the reduction of the intensity of the second positron lifetime associated with vacancy clusters preassembly located at the boundaries of new grains. The determined activation energy of grain migration was equal to 3.12 +/- 0.38 eV, and the recrystallization temperature was established at 700 degrees C. The significant change in the pole figures indicating recrystallization was noticed only at 1100 degrees C, however, the recrystallization process has been confirmed by the differential thermal analysis. In the temperature range from 100 to 1100 degrees C, a continuous decrease of the crystalline lattice strain was observed.
NSTL
Elsevier