Industrial spent MoSi_(2)-based materials were used to fabricate oxidation-resistant coatings on molybdenum via slurry painting in air. The microstructure, phase constituent and high-temperature oxidation behaviors of...Industrial spent MoSi_(2)-based materials were used to fabricate oxidation-resistant coatings on molybdenum via slurry painting in air. The microstructure, phase constituent and high-temperature oxidation behaviors of the coatings at 1500 ℃ were explored. The results show that the bonding layer is generated in the coatings after sintering,which strengthens the metallurgical combination between the coating and the substrate because of the formation of diffusion layers. Rare cracks appear in the coating using pure MoSi_(2)(PM coating) while the coating using spent MoSi_(2)(SM coating) is free of cracks due to decreased thermal expansion mismatch. After oxidation, the oxide scale of PM coating possesses large-sized pores while a relatively dense oxide scale is acquired by SM coating. Compared with PM coating, thinner glassy oxide scale with lower mass gain is obtained by SM coating, exhibiting better anti-oxidation properties at 1500 ℃.展开更多
Porous TiAl3 intermetallics were fabricated through vacuum reactive sintering from Ti-75A1 at.% elemental powder mixture.The phase compositions,expansion behaviors,pore characteristics and microstructure evolution of ...Porous TiAl3 intermetallics were fabricated through vacuum reactive sintering from Ti-75A1 at.% elemental powder mixture.The phase compositions,expansion behaviors,pore characteristics and microstructure evolution of TiAl3 intermetallics were investigated,and the pore formation mechanism was also proposed.It was found that the actual temperature of compacts showed an acute climb from 668 to 1244℃ in 166s,while the furnace temperature maintained the linear growth of 5℃/min,which indicated that an obvious thermal explosion（TE）reaction occurred during sintering,and only single-phase TiA13 intermetallic was synthesized in TE products.The open porosity increased from 22.2（green compact）to 32.8% after reactive diffusion sintering at 600℃ and rised to 58.7% after TE,then decreased to 51.2% after high-temperature homogenization at 1100℃.Therefore,TE reaction is the dominated pore formation mechanism of porous TiAl3 intermetallics.The pore evolution in porous TiAl3 intermetallics occurred by the following mechanisms：certain intergranular pores remained among powder particles of green compact,then low-temperature sintering resulted in a further increase in porosity due to the Kirkendall effect.Moreover,TE reaction gave rise to a dramatic volume expansion because of the rapid increase in temperature,and high-temperature sintering caused densification and a slight shrinkage.展开更多
TiC based cermets were produced with FeCr, as a binder, by conventional P/M （powder metallurgy） to near 〉97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the ...TiC based cermets were produced with FeCr, as a binder, by conventional P/M （powder metallurgy） to near 〉97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of 〉1360℃ caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360℃ for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettabifity of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals.展开更多
The lubrication effectiveness of the composite lubricants, 50wt% ethylene bis-stearamide （EBS） wax ＋50wt% graphite and 50wt% EBS wax ＋ 50wt% BN, during the powder metallurgy （P/M） electrostatic die wall lubricat...The lubrication effectiveness of the composite lubricants, 50wt% ethylene bis-stearamide （EBS） wax ＋50wt% graphite and 50wt% EBS wax ＋ 50wt% BN, during the powder metallurgy （P/M） electrostatic die wall lubrication and warm compaction was studied. The results show that the combination of 50wt% EBS wax and 50wt% graphite has excellent lubrication performance, resulting in fairly high green densities, but the mixture of 50wt% EBS wax and 50wt% BN has less beneficial effect. In addition, corresponding die temperatures should be applied when different die wall lubricants are used to achieve the highest green densities.展开更多
The addition of Cu-10Sn alloy for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated include the sintering temperature, the sintering ti...The addition of Cu-10Sn alloy for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated include the sintering temperature, the sintering time, and the mass percent of Cu-10Sn. For vacuum sintering, effective sintering occurs at temperature between 1 250 ℃ and 1 300 ℃. The maximum sintered density was achieved at 1 300 ℃ for 60 min with 3% （in mass percent） Cu- 10Sn alloy. More than 3% （in mass percent） Cu-10Sn content and temperature above 1 300 ℃ caused slumping of the samples. A maximum density of 7.4 g/cm^3 was achieved with 3% （in mass percent） Cu-10Sn content at a sintering temperature of 1 300 ＂C for 60 rain. A maximum ultimate tensile strength （UTS） of 517 MPa was achieved with 3% （in mass percent） Cu-10Sn content. With content higher than 2% （in mass percent） Cu-10Sn, a maximum increase in the density was observed. The fracture morphologies of the sintered samples are also reported.展开更多
An entropy-stabilized multicomponent ultrahigh-temperature ceramic(UHTC)coating,(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2),on a graphite substrate was in-situ sintered by spark plasma sintering(SPs)from constituent tr...An entropy-stabilized multicomponent ultrahigh-temperature ceramic(UHTC)coating,(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2),on a graphite substrate was in-situ sintered by spark plasma sintering(SPs)from constituent transition metal diboride powders.The(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2) coating had a hardness of 31.2±2.1 GPa and resisted 36.9 GPa of stress before delamination,as observed at the interface.The temperature-dependent thermal properties of the multicomponent diboride(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2) were obtained by molecular dynamics(MD)simulations driven by a machine learning force field(MLFF)trained on density functional theory(DFT)calculations.The thermal conductivity,density,heat capacity,and coefficient of thermal expansion obtained by the MD simulations were used in time-dependent thermal stress finite element model(FEM)simulations.The low thermal conductivity(<6.52 W·m^(-1)·K^(-1))of the multicomponent diboride coupled with its similar coefficient of thermal expansion to that of graphite indicated that stresses of less than 10 GPa were generated at the interface at high temperatures,and therefore,the coating was mechanically resistant to the thermal stress induced during ablation.Ablation experiments at 220℃ showed that the multicomponent diboride coating was resistant to thermal stresses with no visible cracking or delamination.The ablation mechanisms were mechanical denudation and evaporation of B_(2)O_(5) and light V-Ti oxides,which caused a decrease in the mass and thickness of the coating and resulted in mass and linear ablation rates of-0.51 mg·s^(-1) and -1.38μm·s^(-1),respectively,after 60 s.These findings demonstrated the thermal and mechanical stability of multicomponent entropy-stabilized diborides as coatings for carbon materials in engineering components under extreme environments.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 51874305, 51972338)Graduate Research and Innovation Projects of Jiangsu Province, China (No. KYCX21_22413)。
文摘Industrial spent MoSi_(2)-based materials were used to fabricate oxidation-resistant coatings on molybdenum via slurry painting in air. The microstructure, phase constituent and high-temperature oxidation behaviors of the coatings at 1500 ℃ were explored. The results show that the bonding layer is generated in the coatings after sintering,which strengthens the metallurgical combination between the coating and the substrate because of the formation of diffusion layers. Rare cracks appear in the coating using pure MoSi_(2)(PM coating) while the coating using spent MoSi_(2)(SM coating) is free of cracks due to decreased thermal expansion mismatch. After oxidation, the oxide scale of PM coating possesses large-sized pores while a relatively dense oxide scale is acquired by SM coating. Compared with PM coating, thinner glassy oxide scale with lower mass gain is obtained by SM coating, exhibiting better anti-oxidation properties at 1500 ℃.
基金supported by the Fundamental Research Funds for the Central Universities(2017XKQY006)
文摘Porous TiAl3 intermetallics were fabricated through vacuum reactive sintering from Ti-75A1 at.% elemental powder mixture.The phase compositions,expansion behaviors,pore characteristics and microstructure evolution of TiAl3 intermetallics were investigated,and the pore formation mechanism was also proposed.It was found that the actual temperature of compacts showed an acute climb from 668 to 1244℃ in 166s,while the furnace temperature maintained the linear growth of 5℃/min,which indicated that an obvious thermal explosion（TE）reaction occurred during sintering,and only single-phase TiA13 intermetallic was synthesized in TE products.The open porosity increased from 22.2（green compact）to 32.8% after reactive diffusion sintering at 600℃ and rised to 58.7% after TE,then decreased to 51.2% after high-temperature homogenization at 1100℃.Therefore,TE reaction is the dominated pore formation mechanism of porous TiAl3 intermetallics.The pore evolution in porous TiAl3 intermetallics occurred by the following mechanisms：certain intergranular pores remained among powder particles of green compact,then low-temperature sintering resulted in a further increase in porosity due to the Kirkendall effect.Moreover,TE reaction gave rise to a dramatic volume expansion because of the rapid increase in temperature,and high-temperature sintering caused densification and a slight shrinkage.
文摘TiC based cermets were produced with FeCr, as a binder, by conventional P/M （powder metallurgy） to near 〉97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of 〉1360℃ caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360℃ for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettabifity of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals.
基金This work was financially supported by the National High-Tech Research and Development Program of China (863 Program, No.2001AA337010)
文摘The lubrication effectiveness of the composite lubricants, 50wt% ethylene bis-stearamide （EBS） wax ＋50wt% graphite and 50wt% EBS wax ＋ 50wt% BN, during the powder metallurgy （P/M） electrostatic die wall lubrication and warm compaction was studied. The results show that the combination of 50wt% EBS wax and 50wt% graphite has excellent lubrication performance, resulting in fairly high green densities, but the mixture of 50wt% EBS wax and 50wt% BN has less beneficial effect. In addition, corresponding die temperatures should be applied when different die wall lubricants are used to achieve the highest green densities.
文摘The addition of Cu-10Sn alloy for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated include the sintering temperature, the sintering time, and the mass percent of Cu-10Sn. For vacuum sintering, effective sintering occurs at temperature between 1 250 ℃ and 1 300 ℃. The maximum sintered density was achieved at 1 300 ℃ for 60 min with 3% （in mass percent） Cu- 10Sn alloy. More than 3% （in mass percent） Cu-10Sn content and temperature above 1 300 ℃ caused slumping of the samples. A maximum density of 7.4 g/cm^3 was achieved with 3% （in mass percent） Cu-10Sn content at a sintering temperature of 1 300 ＂C for 60 rain. A maximum ultimate tensile strength （UTS） of 517 MPa was achieved with 3% （in mass percent） Cu-10Sn content. With content higher than 2% （in mass percent） Cu-10Sn, a maximum increase in the density was observed. The fracture morphologies of the sintered samples are also reported.
基金This work was supported by the Swedish Foundation for Strategic Research(SSF)for Infrastructure Fellowship(No.RIF14-0083)The authors thank Lars Frisk for the ablation setup and testing and for the coefficient of thermal expansion measurements.The authors also acknowledge the Lulea Material Imaging and Analysis(LUMIA)Center for providinggthe imaging characterization equipment.Daniel’Hedman acknowledges financial support from the Institute for Basic Science,Republic of Korea(No.IBS-RO19-DI)+1 种基金The authors would like to acknowledge the computational resources provided by the National Academic Infrastructure for Supercomputing in Sweden(NAISS)via the NAISS 2023/3-31 and NAISS 2023/6-292 projects,which were partially funded by the Swedish Research Council(No.2022-06725)In addition,computational resources were provided by the Institute for Basic Science(Republic of Korea)at the HPC clusters Cimulator(CMCM,Ulsan)and Olaf(IBS-HQ,Daejeon).
文摘An entropy-stabilized multicomponent ultrahigh-temperature ceramic(UHTC)coating,(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2),on a graphite substrate was in-situ sintered by spark plasma sintering(SPs)from constituent transition metal diboride powders.The(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2) coating had a hardness of 31.2±2.1 GPa and resisted 36.9 GPa of stress before delamination,as observed at the interface.The temperature-dependent thermal properties of the multicomponent diboride(Ti_(0.25)V_(0.25)Zr_(0.25)Hf_(0.25))B_(2) were obtained by molecular dynamics(MD)simulations driven by a machine learning force field(MLFF)trained on density functional theory(DFT)calculations.The thermal conductivity,density,heat capacity,and coefficient of thermal expansion obtained by the MD simulations were used in time-dependent thermal stress finite element model(FEM)simulations.The low thermal conductivity(<6.52 W·m^(-1)·K^(-1))of the multicomponent diboride coupled with its similar coefficient of thermal expansion to that of graphite indicated that stresses of less than 10 GPa were generated at the interface at high temperatures,and therefore,the coating was mechanically resistant to the thermal stress induced during ablation.Ablation experiments at 220℃ showed that the multicomponent diboride coating was resistant to thermal stresses with no visible cracking or delamination.The ablation mechanisms were mechanical denudation and evaporation of B_(2)O_(5) and light V-Ti oxides,which caused a decrease in the mass and thickness of the coating and resulted in mass and linear ablation rates of-0.51 mg·s^(-1) and -1.38μm·s^(-1),respectively,after 60 s.These findings demonstrated the thermal and mechanical stability of multicomponent entropy-stabilized diborides as coatings for carbon materials in engineering components under extreme environments.
