The dissolving behaviour of Nb and Ti carbonitride precipitates inmicroalloyed steels during isothermal holding at 1300℃ was investigated by Transmission electronmicroscopy (TEM) and energy dispersion x-ray spectrum ...The dissolving behaviour of Nb and Ti carbonitride precipitates inmicroalloyed steels during isothermal holding at 1300℃ was investigated by Transmission electronmicroscopy (TEM) and energy dispersion x-ray spectrum (EDX). It was found that all precipitates inNb-Ti microalloyed steel are (Nb, Ti)(C, N). With holding time increasing, the atomic ratio of Nb/Tiin precipitates decrease gradually. These precipitates still existe even after holding for 48 h at1300℃ while Nb(C, N) precipitates dissolve away in Nb microalloyed steel only after 4 h at the sametemperature. These results show that formation and thermostability of precipitates are considerablyinfluenced by interaction between Nb and Ti.展开更多
The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers.However,the process of adding whiskers or nanoparticles has the disadvantages of h...The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers.However,the process of adding whiskers or nanoparticles has the disadvantages of high cost and health hazard as well as the agglomeration;although a new in-situ two-step sintering process can solve the above problems to some extent,yet the problems of low conversion ratio of the raw materials and the abnormal grain growth exist in this process.In this paper,an in-situ one-step synthesis technology is proposed,which means the growth of whiskers or nanoparticles and the sintering of the compact can be accomplished by one time in furnace.A kind of Ti（C,N）-based ceramic cutting tool material synergistically toughened by TiB_2 particles and whiskers is fabricated with this new process.The phase compositions,relationships between microstructure and mechanical properties as well as the toughening mechanisms are analyzed by means of X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The composite which is sintered under a pressure of 32 MPa at a temperature of 1700℃in vacuum holding for 60 min can get the optimal mechanical properties.Its flexural strength,fracture toughness and Vickers hardness are 540 MPa,7.81 MPa·m（1/2）and 20.42 GPa,respectively.The composite has relatively high density,and the in-situ synthesized TiB_2 whiskers have good surface integrity,which is beneficial for the improvement of the fracture toughness.It is concluded that the main toughening mechanisms of the present composite are whiskers pulling-out and crack deflection induced by whiskers,crack bridging by whiskers/particles and multi-scale particles synergistically toughening.This study proposes an in-situ one-step synthesis technology which can be well used for fabricating particles and whiskers synergistically toughened ceramic tool materials.展开更多
(Ti, Nb)C-Ni composite is prepared. The analyses of SEM, EPMA and TEM/EDAX show that (Ti, Nb)C-Ni consists of three phases,which are called interior, transitional and Ni phases respectively. Several models are calcula...(Ti, Nb)C-Ni composite is prepared. The analyses of SEM, EPMA and TEM/EDAX show that (Ti, Nb)C-Ni consists of three phases,which are called interior, transitional and Ni phases respectively. Several models are calculated by self-consistent-field variational X alpha(SCF-DV-X alpha) method, one of the quantum chemistry calculating methods. The calculated results show that when Ni element increases, the bond orders (measures of strength of covalent bonding) of Ti-C and Ni-C in the models decrease correspondingly, which is to say that there is a gradient variation of the covalent bond in the transitional phase which is compatible with both the interior and Ni phases. It is beneficial for improving the mechanical properties of the materials.展开更多
Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength...Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength Low Alloy) steel. The strain induced precipitationoccurred during the isothermal relaxation stage after deformed in the non-recrystallizationtemperature region. After 30% predeformation at 850 and 900℃, there are two kinds of particles,(Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles riseswith the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in thelattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in theprecipitates increases with the relaxation time. The results were compared with the refinementeffect of microstructures caused by relaxation-precipitation controlling transformation (RPC)processing.展开更多
Fe-based alloy coatings reinforced by Ti（ C, N） particles was produced through CO2 laser cladding technology. The microstructure of laser cladding coating was analyzed by means of X-ray diffraction （ XRD ）, transm...Fe-based alloy coatings reinforced by Ti（ C, N） particles was produced through CO2 laser cladding technology. The microstructure of laser cladding coating was analyzed by means of X-ray diffraction （ XRD ）, transmission electron microscopy （TEM） , selected area electron diffraction （ SAED ） , scanning electron microscopy （SEM） and electron probe microscopic analyzer （ EPMA ）. The mechanical property of the layer was measured by using microhardness meter. The results show that Ti （ C0. 3 N0. 7 ） panicles are introduced by an in-situ metallurgical reaction between TiN particle and graphite powder during laser cladding process. Titanium carbonitrides particles existed in the layer are fairly fine, ranging from 0. 1 μm to 5.0 μm, and evenly dispersed in the metal α-Fe matrix. Most of them take on nearly rhombus shape, and some of them are irregular in shape. The microhardness of laser cladding layer ranges from 770 HV0. 3 to 850 HV0. 3.展开更多
简述了微合金钢中微量元素 Nb 的主要作用,回顾了应变诱导析出的研究方法及优缺点,阐明了变形奥氏体应变诱导析出相的种类,晶体结构,析出相的形成顺序、形貌和分布,分析了影响析出动力学的主要因素并简要介绍了应变诱导析出动力学模型...简述了微合金钢中微量元素 Nb 的主要作用,回顾了应变诱导析出的研究方法及优缺点,阐明了变形奥氏体应变诱导析出相的种类,晶体结构,析出相的形成顺序、形貌和分布,分析了影响析出动力学的主要因素并简要介绍了应变诱导析出动力学模型的最新发展。展开更多
基金The work was financially supported by National Key Basic Research and Development Program of China (No. G1998061507)
文摘The dissolving behaviour of Nb and Ti carbonitride precipitates inmicroalloyed steels during isothermal holding at 1300℃ was investigated by Transmission electronmicroscopy (TEM) and energy dispersion x-ray spectrum (EDX). It was found that all precipitates inNb-Ti microalloyed steel are (Nb, Ti)(C, N). With holding time increasing, the atomic ratio of Nb/Tiin precipitates decrease gradually. These precipitates still existe even after holding for 48 h at1300℃ while Nb(C, N) precipitates dissolve away in Nb microalloyed steel only after 4 h at the sametemperature. These results show that formation and thermostability of precipitates are considerablyinfluenced by interaction between Nb and Ti.
基金Supported by National Natural Science Foundation of China(Grant No.51175305)Key Special Project of Numerical Control Machine Tool of China(Grant No.2012ZX04003-051)China Postdoctoral Science Special Foundation(Grant No.2012T50610)
文摘The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers.However,the process of adding whiskers or nanoparticles has the disadvantages of high cost and health hazard as well as the agglomeration;although a new in-situ two-step sintering process can solve the above problems to some extent,yet the problems of low conversion ratio of the raw materials and the abnormal grain growth exist in this process.In this paper,an in-situ one-step synthesis technology is proposed,which means the growth of whiskers or nanoparticles and the sintering of the compact can be accomplished by one time in furnace.A kind of Ti（C,N）-based ceramic cutting tool material synergistically toughened by TiB_2 particles and whiskers is fabricated with this new process.The phase compositions,relationships between microstructure and mechanical properties as well as the toughening mechanisms are analyzed by means of X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The composite which is sintered under a pressure of 32 MPa at a temperature of 1700℃in vacuum holding for 60 min can get the optimal mechanical properties.Its flexural strength,fracture toughness and Vickers hardness are 540 MPa,7.81 MPa·m（1/2）and 20.42 GPa,respectively.The composite has relatively high density,and the in-situ synthesized TiB_2 whiskers have good surface integrity,which is beneficial for the improvement of the fracture toughness.It is concluded that the main toughening mechanisms of the present composite are whiskers pulling-out and crack deflection induced by whiskers,crack bridging by whiskers/particles and multi-scale particles synergistically toughening.This study proposes an in-situ one-step synthesis technology which can be well used for fabricating particles and whiskers synergistically toughened ceramic tool materials.
文摘(Ti, Nb)C-Ni composite is prepared. The analyses of SEM, EPMA and TEM/EDAX show that (Ti, Nb)C-Ni consists of three phases,which are called interior, transitional and Ni phases respectively. Several models are calculated by self-consistent-field variational X alpha(SCF-DV-X alpha) method, one of the quantum chemistry calculating methods. The calculated results show that when Ni element increases, the bond orders (measures of strength of covalent bonding) of Ti-C and Ni-C in the models decrease correspondingly, which is to say that there is a gradient variation of the covalent bond in the transitional phase which is compatible with both the interior and Ni phases. It is beneficial for improving the mechanical properties of the materials.
基金This work was financially supported by the national key basic research and development program of China (No.G1998061507).
文摘Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength Low Alloy) steel. The strain induced precipitationoccurred during the isothermal relaxation stage after deformed in the non-recrystallizationtemperature region. After 30% predeformation at 850 and 900℃, there are two kinds of particles,(Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles riseswith the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in thelattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in theprecipitates increases with the relaxation time. The results were compared with the refinementeffect of microstructures caused by relaxation-precipitation controlling transformation (RPC)processing.
文摘Fe-based alloy coatings reinforced by Ti（ C, N） particles was produced through CO2 laser cladding technology. The microstructure of laser cladding coating was analyzed by means of X-ray diffraction （ XRD ）, transmission electron microscopy （TEM） , selected area electron diffraction （ SAED ） , scanning electron microscopy （SEM） and electron probe microscopic analyzer （ EPMA ）. The mechanical property of the layer was measured by using microhardness meter. The results show that Ti （ C0. 3 N0. 7 ） panicles are introduced by an in-situ metallurgical reaction between TiN particle and graphite powder during laser cladding process. Titanium carbonitrides particles existed in the layer are fairly fine, ranging from 0. 1 μm to 5.0 μm, and evenly dispersed in the metal α-Fe matrix. Most of them take on nearly rhombus shape, and some of them are irregular in shape. The microhardness of laser cladding layer ranges from 770 HV0. 3 to 850 HV0. 3.
