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The bending strength of ultrafine-grained cemented carbides exceeds that of medium-grained cemented carbides. This was thought to be due to the smaller size of defects within the ultrafine-grained cemented carbides. However, this attribution had not been verified because the specimens broke into numerous small pieces during bending tests. In addition, previous studies on the bending strength of medium-grained cemented carbides reported that there is limiting strength which is a region of not increasing bending strength by reducing the defect size. Therefore, in this study, we conducted the tensile test, which is unlikely to produce many small pieces, and the bending test to determine the cause of the high strength in ultrafine-grained cemented carbides. The ratio of bending strength to tensile strength was comparable between the medium- and ultrafine-grained cemented carbides. The number of fragments produced by fractures were almost same between the medium- and ultrafinegrained cemented carbides in case of the almost same strength. It was clear that the tensile strength of both medium- and ultrafine-grained cemented carbides increased as the defect size decreased with no sign of limiting strength. These results suggest that further strength improvements can be achieved by controlling defect size in ultrafine-grained cemented carbides. [ABSTRACT FROM AUTHOR]

Monte Carlo simulation was performed to investigate the effect of sintering on the changes in microstructure, porosity, and pore distribution of thermal barrier coating layers synthesized by electron beam physical vapor deposition. First, the simulation well expressed the characteristic porous structures such as columnar and featherlike structures, which were fabricated under the condition of substrate rotation. Secondly, the sintering of such a porous structure by high-temperature annealing could be demonstrated using the simulation. The microstructure of the layer close to the substrate surface shows fine grains and pores, suggesting ease of sintering and grain growth, which is clearly demonstrated from the experimental results of the yttria-stabilized zirconia layer deposited by electron beam physical vapor deposition. The simulation also reveals the sintering behavior of the porous including heterogeneous structure and pore distribution. By introducing a small sintering step to the deposition process during the simulation, the experimental values of the porosity observed in the layers could be successfully explained. The doubled effects of sintering on porosity during both deposition and exposure to high temperature environment enhanced the heterogeneity of the microstructures of the layers. [ABSTRACT FROM AUTHOR]

Powder metallurgy is a process for compacting and sintering powders such as metals and ceramics, and has been attracting new attention in recent years. This paper presents research examples in which simulation methods such as molecular dynamics (MD) method, Monte Carlo (MC) method, finite element method (FEM), and discrete element method (DEM) are applied to powder metallurgy. The MD method is used to calculate physical property values such as interfacial energy and diffusion coefficient that change depending on the type of grain boundaries. The MC method is used to calculate the microstructural development due to the sintering and grain growth. The microstructure can be predicted when the sintering process is changed. The FEM is used to calculate deformation and strain. The sintering simulation combined with the MC method can calculate the microstructural changes and deformation simultaneously. In the compaction simulation, density distribution due to the friction with the mold can be analyzed. The DEM is used to calculate the compaction structure. The interaction of the friction and stiffness between particles and particle/mold can be analyzed. As powder metallurgy technology develops, process design that considers the whole process will be important. Supporting technology based on simulation will become increasingly important. [ABSTRACT FROM AUTHOR]

In order to investigate the cause of the liquid phase migration (LPM) and the shape distortion when WC-Co cemented carbides (alloys) undergo a temperature gradient during cooling, round bars of WC-10 mass%Co alloys are inserted halfway under the coil of the induction heating furnace and partially heated at 1673 K. The results showed that Co migrated from the higher temperature side to the lower one and increase of Co content and bar diameter occurred in a zone at the outside of the coil. The alloy containing free carbon had a significantly narrow Co-increased zone and the zone located at a lower temperature. The volume transfer (V) of Co during heating changed in proportional to the square root of the heating time (t). It was considered that the phenomenon was the same as the LPM between a couple of alloys having different Co content in our previous report. We have concluded that the Co-increased zone in this study corresponds to the Co solid-liquid coexistence zone during partial heating and the Co increase is caused by the migration pressure occurred in the zone, which we named ΠSL. ΠSL should be generated because FWC/Co(S) derived from γWC/Co(S) and γCo(L)/Co(S) is higher than FWC/Co(L) derived from γWC/Co(L). [ABSTRACT FROM AUTHOR]

The simulation for sintering of co-firing double layer compacts and substrate-constrained compacts were obtained by coupled Monte Carlo method and finite element method. In the coupled simulation of a co-firing compacts with different sintering shrinkage curves, the amount of warpage during and after sintering changed significantly. As a result of detailed confirmation of the results, it was found that there was a difference between the porosity obtained by the Monte Carlo method and by finite element method, so the coupled simulation was modified to minimize the porosity difference. As a result of the coupled simulation of constraint sintering, it was not contracted in the surface direction, but only in the thickness direction, and the results were represented in the previous experimental results. We found that coupled simulation can be applied as a tool to design and analyze the sintering behavior of products obtained by co-firing and constrained sintering. [ABSTRACT FROM AUTHOR]

Ultrafine-grained binderless cemented carbides using 0.4 µm WC particles were prepared by adding Cr3C2, VC, TaC, βt and various sizes of Ti(C,N) particles. SEM observations of the polished and fractured surfaces revealed that the WC grains became finer after the addition of the carbides or carbonitrides. In the Ti(C,N)-added binderless cemented carbides, the WC grains became finer with decreasing Ti(C,N) particle size and increasing Ti(C,N) content. The grain size of WC in the binderless cemented carbide containing 0.1 μm Ti(C,N) was comparable to that of the Cr3C2-containing binderless cemented carbide, although not as fine as that of the VC-containing binderless cemented carbide. The binderless cemented carbides containing fine Ti(C,N) grains were harder and had higher strengths than the other carbides. The combined addition of fine Ti(C,N) and Cr3C2 resulted in more homogeneous WC grains. These results indicate that the grain growth inhibition of binderless cemented carbides varies depending on the type and grain size of the added carbonitrides. These findings will contribute to the future development of binderless cemented carbides. [ABSTRACT FROM AUTHOR]

WC-Ti(C,N)-Cr3C2-Co ultrafine-grained cemented carbides with different contents of C, N and Co binder phases were fabricated. Their microstructures and mechanical properties were examined, and the relationship between the existing form of Ti(C,N) and various conditions was mainly discussed. The hardness of the samples increased and their fracture toughness decreased with decreasing C content. The average T.R.S. peaked at 4.8 GPa on the low-C side. Their microstructures significantly changed when the N2 partial pressure changed. At a N2 partial pressure of 2.6 kPa, the microstructure became finer and the average T.R.S. was the highest. Meanwhile, at N2 partial pressures of 0 and 11.7 kPa, the microstructure became coarser and the average T.R.S. decreased. As the content of Co binder phase decreased, the number of WC/WC interfaces increased. The average T.R.S. was maximum at 16.4 vol% Co, and decreases with the Co content, but was higher than those of conventional cemented carbides. The existing form of Ti(C,N) changed depending on the N content. Herein, a N2 partial pressure of 2.6 kPa and low C contents were deemed optimal. [ABSTRACT FROM AUTHOR]

In shis study, yield stress equation, flow rules and physical properties of barium titanate (BaTiO3) are experimentally obtained. These basic equations and coefficient of flow stress are introduced to finite element method and sintering behavior of barium titanate bulk is simulated. From the uni-axis compression test, yield stress equation of BaTiO3 is expressed by Shima's equation and flow rule is written by plastic equiation. The coefficient of flow stress of BaTiO3 is significantly smaller than literature Alumina and the value is different when the grain size is different. The experimental sintering deformation is quantitatively reproduced by numerical simulation, where basic equation and physical properties are exprerimentally introduced. In addition, the coefficient of flow stress could be determined by simulation sensitivily analysis. Through this study, experimentally obtained yield stress equation, flow rules and coefficient of flow stress are numerically validated. [ABSTRACT FROM AUTHOR]

Ground round bars made of WC-20 mass%Co cemented carbides were used to accurately determine the changes in shape. The bars were heated at 1673 K and cooled under different conditions to investigate the changes in Co content and diameter (d) in the longitudinal direction. When the bars were heated in a conventional sintering furnace, rapid cooling increased the Co content and d at both ends, while slow cooling increased those at the center. In the latter case, the amount of change was smaller. When the bar was heated using a tubular furnace and then cooled under 30 K of temperature gradient in the longitudinal direction, the Co content and d on the higher temperature side decreased and those on lower temperature side increased. The relationship between the change in Co content and the change in d could be explained quantitatively by considering the migration of the liquid phase in the temperature range of solid-liquid Co coexistence region. This study revealed that when WC-Co cemented carbides were fabricated using the conventional sintering furnace, an inevitable temperature gradient in the specimen during cooing caused the liquid phase migration and the shape distortion, regardless of the cooling rate. [ABSTRACT FROM AUTHOR]

The fracture of WC-Co cemented carbides with different WC particle sizes was investigated experimentally, and then a discrete element method (DEM) simulation was performed considering such experiments. The bending strength of ultra-fine grained cemented carbide with a WC particle size of 0.4 μm was extremely high. The ultrafine grained cemented carbide sample after bending test had numerous fracture pieces and the short length of the specimens without fracture. Initial structures consisting of matrix and defect (d) particles were used in the DEM simulations. The DEM simulation results for a sample of 2% d particle, which was considered ultra-fine grained cemented carbide by comparison with experimental results, were as follows: The sample with the highest load at fracture, the most d particle bond-breaking, and the shortest length of remaining specimen without particle bond breaking was the 2% d sample. The DEM simulation was considered to be very useful in understanding the ultrafine grained cemented carbide’s strength and fracture behavior. [ABSTRACT FROM AUTHOR]

Liquid phase sintering behavior of metal-glass system is experimentally and numerically analyzed. From the experimental observation, glass wets metal surfaces and assists the metal particles rearrangement, which is very important for annihilating pores. From the experiment, the amount of glass influences not only on the porosity but also on the grain growth behavior significantly. The sintering behavior is well reproduced by computational study by using Monte Carlo method with experimentally obtained surface energies of metal-glass system. The numerical study suggests that the frequency factor of Ostwald should be smaller than that of solid grain growth in this metal-glass powder system. Finally, this study suggests that spatial distribution is very important for grain growth. Although glass prevents the metal particle contact, the glass assists the metal particles rearrangement that contributes to metal grain growth. [ABSTRACT FROM AUTHOR]

Joined plates of WC-Co cemented carbides with different Co content, WC grain size and carbon content were fabricated by sintering, grinding into rectangular plates, and then reheating (joining) the two plates together. Distribution of Co, microstructure and shape of such joined plates were investigated in detail. It was confirmed that Co migrated from higher Co content to lower one, from coarser WC grains to finer ones and from higher carbon content to lower one as shown in previous studies by Lisovsky and Fang. Shapes of the joined plates were distorted caused by volume change of each plate resulting from migration of liquid Co and solute WC through the interface of the joined plates. In the joined plates with different Co content, Co distributed discontinuously at the interface. This result can be explained by the fact that Co content at the both sides of the interface had been almost fixed just after two faces were joined. This study was done under the special condition using joined plates, but the results obtained suggest that the shape of industrial-made WC-Co cemented carbides should be distorted when distribution of Co becomes non uniform. [ABSTRACT FROM AUTHOR]

The sintering and grain growth behavior of alumina with different grain sizes was investigated experimentally and by Monte Carlo simulations. The densification and grain growth of alumina particles increased with increasing sintering temperature. This effect was more significant for fine alumina particles. The grain size in the sintered body obtained from fine particles was larger than that obtained from coarse particles. These experimental results were successfully reproduced by Monte Carlo simulations. The relationship between simulation parameters (frequency factors for pore sink, high diffusion, and grain growth), which were introduced in the simulation by adapting the experimental results, and the coefficients of diffusion (lattice diffusion, surface diffusion, and grain boundary diffusion) of alumina were also discussed in this study. [ABSTRACT FROM AUTHOR]

WC-Co ultrafine-grained cemented carbide with the combined addition of Ti(C,N) and Cr3C2 was studied for microstructure and mechanical properties. In particular, the strength (transverse rupture strength) of the alloy was examined in detail comparing it with other kinds of cemented carbides. The WC grain size of the alloy with the single addition of Ti(C,N) or Cr3C2 became finer with increasing the amount of the additive. The combined addition of Ti(C,N) and Cr3C2 made the WC grain size further finer and the microstructure more homogeneous. The hardness of Ti(C,N)-Cr3C2 added alloys increased with decreasing the average grain size of WC or the mean free path of the binder phase, but the fracture toughness decreased. The strength of Ti(C,N)-Cr3C2 added alloy varied depending on the amount of the additive. It was noted that the strength of 3 vol%Ti(C,N)-0.5 vol%Cr3C2 alloy was the best and reached 4.6 GPa on average and 5.0 GPa at the maximum. It was observed that such a high strength alloy was shattered after the transverse rupture strength test and so that it was difficult to detect the fracture origin. Based on the limiting strength that is generated in normal-grained cemented carbide, it was considered that a high strength level exceeding the limiting strength of normal-grained alloy was achieved in the ultrafine-grained cemented carbide obtained in this study. The WC-Co ultrafine-grained cemented carbide with Ti(C,N)-Cr3C2 was superior in strength compared to conventional cemented carbide. New applications can be expected to take advantage of these characteristics. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were performed to study six grain boundaries of α-alumina (Al2O3) with a glassy phase of anorthite (CaAl2Si2O8) composition. We calculated excess energy, diffusion constant and ratio of excess volume with different thickness of the glassy film. It was found that excess energy for some grain boundaries exhibited a minimum. When the thickness of the glassy film was thick adequately, excess energy corresponded to the energy of alumina-glass interface and they were different for each interface. Diffusion constants depended on the thickness of the glassy film. The diffusion constant of thin film was smaller than that of thick film. Excess volume was the maximum when the thickness of the glassy film was 0.2~0.3 nm. When the atomic arrangement of the crystals didn't fit each either, the excess volume of the grain boundary with the glassy film was smaller than that of the pure grain boundary. When the glassy film width was nm order, the atomic arrangement of the glassy phase was regular and the atomic diffusion behavior was approached that of a solid (crystalline) phase. We need to consider not only solid-liquid interface but also solid-solid (crystalline) interface for the structure of ceramics made by liquid phase sintering. [ABSTRACT FROM AUTHOR]

The simulation for liquid phase sintering has been newly developed by Monte Carlo method. The basic three mechanisms in liquid phase sintering, namely (1) liquid wetting on solid surface, (2) rearrangement of solid particle by capillary force of liquid, (3) growth of solid particles by solution-reprecipitation through liquid phase (Ostwald ripening), have been introduced in the simulation. The liquid wetting on a solid plane or solid particle surface progressed more easily as decreasing the energy between solid and liquid (γSL). The introduction of rearrangement into the simulation brought the result that relative density increased with decreasing γSL and pores remained. The introduction of Ostwald ripening in addition to liquid wetting and rearrangement produced the result that relative density increased on the whole and the effect of γSL became clear. The simulation including Ostwald ripening was able to demonstrate clearly and continuously the influence of γSL on growth and contiguity of solid particles. [ABSTRACT FROM AUTHOR]

The WC-Co cemented carbides with the addition of Ti(C,N) base particles with different sizes were fabricated by liquid phase sintering and their microstructures were mainly investigated in detail comparing the microstructure of the alloys with VC and Cr3C2 addition. It was found that the WC grain growth was more strongly inhibited with increasing Ti(C,N) content and with decreasing Ti(C,N) particle size. The degree of inhibition by the addition of Ti(C,N) particle with about 0.1 μm size was lower than that of VC addition and was almost same as that of Cr3C2 addition. Considering the results about the relationship between WC grain size and Ti(C,N) particle size and the analysis of Co phase composition, it was seen that the mechanism of grain growth inhibition by the addition of Ti(C,N) particles was the pinning (Zener) effect by the second phase particle, which was different from the mechanism for the addition of VC and Cr3C2 reported previously. The case that one Ti(C,N) particle contacts plural WC grains was often observed, so that the pinning effect was considered to work by many Ti(C,N) particles neighboring one WC grain. The very important result that the pinning effect by Ti(C,N) addition enable to develop the new type of ultra-fine cemented carbide was obtained in this study. [ABSTRACT FROM AUTHOR]

Thermal cracking is one mechanism whereby tool degradation occurs. The establishment of an evaluation method for thermal cracking is important in order to develop tool materials with high performance. The thermal shock of tool materials was investigated by repetitive laser irradiation, in particular for Ti(C,N)-based cermets. It was found that the deformation of cermets increased with increasing irradiation power. The present results confirmed that repetitive laser irradiation is effective for assessing the damage behavior of tool materials. [ABSTRACT FROM AUTHOR]

Wire drawing dies and specimens of WC-Co cemented carbides containing TaNbC or Cr3C2 were fabricated by hot isostatic press (HIP) treatment at 1633 K in 40 MPa Ar and by anneal treatment 1593 K in vacuum. The lifetime of steel code wire drawing were evaluated for the dies and mechanical properties such as hardness, transverse-rupture strength and fracture toughness were examined for the specimens. It is noted that the lifetime of drawing die was remarkably improved by the anneal treatment for both of TaNbC and Cr3C2 containing WC-Co cemented carbides. The TaNbC containing alloys showed longer lifetime than the Cr3C2 containing alloys. The lifetime of drawing die had weak relationship to hardness, but seemed to have no correlation with strength and toughness. The remarkable improvement of drawing die lifetime by the annealing treatment after HIP and the longer lifetime for TaNbC containing alloys can be understood from the viewpoint of adhesion strength between WC and Co phase affected by alloy content and heat treatment of cemented carbides. [ABSTRACT FROM AUTHOR]

Titanium carbonitride (Ti(C,N))-based cermets have been studied for applying them to cutting tools and wearresistant tools. Thermal shock resistance is an important property of tool materials used in severer thermal environment. However, evaluation method of thermal shock resistance has not been sufficiently established for cermets. In order to develop a method to evaluate the thermal shock resistance, irradiation experiments using a laser were conducted; laser beam was irradiated on the surface of thin specimens. The experimental results indicate that deformation of cermets by irradiation depends on the thermal properties, the mechanical properties and the plasticity of specimen. It is thought that the relationships between the deformation and the maximum temperature of cermets during irradiation characterize the material behavior under thermal shock environment. [ABSTRACT FROM AUTHOR]