TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening a...TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening and grain refining effects.In this work,the destabilization mechanisms of the TiC_(x)particles in Al-Si alloy melt with a composition of Al-7Si-7.5TiC were explored via experiments,first-principles calculations and thermodynamic calculations.The experimental results show that Si atoms diffuse into TiC_(x)and Ti atoms are released into the Al melt to form a Ti-rich transition zone during the insulation of TiC_(x)in Al-Si melt,and the TiAlySiz and Al_(4)C_(3)phases are solidified in the Ti-rich zone and at Ti-rich zone/TiC_(x)interface,respectively.The first principles calculations show that the low formation energy of C vacancies facilitates the rapid diffusion of Si atoms in TiC_(x),while the doping of Si atoms reduces the energy barrier of diffusion of Ti atoms in TiC_(x)and promotes the formation of Ti-rich zones.The thermodynamic calculations show that the wide crystallization temperature range of the destabilized product TiAlySiz phase is the key to continuous decomposition of TiC_(x)particles.In addition,the driving force of the main destabilization reaction of TiC_(x)in the Al-Si alloys is about 44 times higher than that in the Al alloys without Si addition.This indicates that the presence of solute Si remarkably promotes the subsequent decomposition process of TiC_(x)in the Al-Si alloy melts.展开更多
Novel Co_(0.3)Cr_(0.7)O_(x)(x=2-3)particles with spinel structure were synthesized via precipitation method through the reactions among CoSO_(4),Cr(NO3)_(3)and NaOH solutions,followed by spray-drying and sintering at ...Novel Co_(0.3)Cr_(0.7)O_(x)(x=2-3)particles with spinel structure were synthesized via precipitation method through the reactions among CoSO_(4),Cr(NO3)_(3)and NaOH solutions,followed by spray-drying and sintering at 1200℃for 4h in the air.The particles were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM).The XRD results revealed that the particles are composed of Co_(0.3)Cr_(0.7)O_(x)phase without the presence of other phases.The SEM observation showed that the particles are in the shape of sphere with well flowability.Infrared radiation test indicated that the total infrared normal emissivity of the coating made of Co_(0.3)Cr_(0.7)O_(x)can be up to 0.92 at 800℃.And the normal emissivities of the prepared Co_(0.3)Cr_(0.7)O_(x)particles are always slightly larger than those of CoCr2O4 particles prepared by solid-state reaction method in the test temperature range of 50-300℃.The relatively high thermal emissivity of Co_(0.3)Cr_(0.7)O_(x)is assumed to be mainly attributed to the spinel structure.These results indicated that Co_(0.3)Cr_(0.7)O_(x)particles are a good thermal radiation material,which can be used as infrared radiation layer in thermal protection system.展开更多
Effect of TiO x particle on grain refining of HAZ during the welding thermal cycle was analyzed.It shows that HAZ would have better post-welding low temperature toughness if it contains plenty of TiO x particles.This ...Effect of TiO x particle on grain refining of HAZ during the welding thermal cycle was analyzed.It shows that HAZ would have better post-welding low temperature toughness if it contains plenty of TiO x particles.This phenomenon can be explained by the following aspects.As we know,welding thermal cycle include a rapid heating process and a cooling process.During the heating-up period,high melting TiO x particles which contains NbC with the size below 1μm can make a stronger pining force on the gain boundary migration than pure NbC ones,this effect restrain the austenite growth and control the austenite grain size to a certain extent.Then,when the cooling process begins,TiO x particles containing MnS with the size between 1 to 3μm act as a nucleation site for the intragranular acicular ferrite (IAF).Although the growth of bainite would extrude the IAF and make the smooth edge of IAF deformed,it still can not grow through the IAF.Just owing to the pining effect of TiO x-NbC particles and the hindering effect of IAF induced by the TiO x-MnS particles,prior austenite grains haven’t undergone a rapid growth during the heating process and these austenite grains are divided into small regions by the IAF finally.展开更多
基金the financial supported from the Key R&D Program of Shaanxi Province,China(No.2020ZDLGY13-01)the innovation team program of material developing and application of key engine components(No.K20220185)the National Natural Science Foundation of China(Nos.52101049,52234009 and 52071262).
文摘TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening and grain refining effects.In this work,the destabilization mechanisms of the TiC_(x)particles in Al-Si alloy melt with a composition of Al-7Si-7.5TiC were explored via experiments,first-principles calculations and thermodynamic calculations.The experimental results show that Si atoms diffuse into TiC_(x)and Ti atoms are released into the Al melt to form a Ti-rich transition zone during the insulation of TiC_(x)in Al-Si melt,and the TiAlySiz and Al_(4)C_(3)phases are solidified in the Ti-rich zone and at Ti-rich zone/TiC_(x)interface,respectively.The first principles calculations show that the low formation energy of C vacancies facilitates the rapid diffusion of Si atoms in TiC_(x),while the doping of Si atoms reduces the energy barrier of diffusion of Ti atoms in TiC_(x)and promotes the formation of Ti-rich zones.The thermodynamic calculations show that the wide crystallization temperature range of the destabilized product TiAlySiz phase is the key to continuous decomposition of TiC_(x)particles.In addition,the driving force of the main destabilization reaction of TiC_(x)in the Al-Si alloys is about 44 times higher than that in the Al alloys without Si addition.This indicates that the presence of solute Si remarkably promotes the subsequent decomposition process of TiC_(x)in the Al-Si alloy melts.
基金National Natural Science Foundation of China(51001093)the Innovation Fund Project of Chinese Academy of Science(ZKYCX08D05)
文摘Novel Co_(0.3)Cr_(0.7)O_(x)(x=2-3)particles with spinel structure were synthesized via precipitation method through the reactions among CoSO_(4),Cr(NO3)_(3)and NaOH solutions,followed by spray-drying and sintering at 1200℃for 4h in the air.The particles were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM).The XRD results revealed that the particles are composed of Co_(0.3)Cr_(0.7)O_(x)phase without the presence of other phases.The SEM observation showed that the particles are in the shape of sphere with well flowability.Infrared radiation test indicated that the total infrared normal emissivity of the coating made of Co_(0.3)Cr_(0.7)O_(x)can be up to 0.92 at 800℃.And the normal emissivities of the prepared Co_(0.3)Cr_(0.7)O_(x)particles are always slightly larger than those of CoCr2O4 particles prepared by solid-state reaction method in the test temperature range of 50-300℃.The relatively high thermal emissivity of Co_(0.3)Cr_(0.7)O_(x)is assumed to be mainly attributed to the spinel structure.These results indicated that Co_(0.3)Cr_(0.7)O_(x)particles are a good thermal radiation material,which can be used as infrared radiation layer in thermal protection system.
文摘Effect of TiO x particle on grain refining of HAZ during the welding thermal cycle was analyzed.It shows that HAZ would have better post-welding low temperature toughness if it contains plenty of TiO x particles.This phenomenon can be explained by the following aspects.As we know,welding thermal cycle include a rapid heating process and a cooling process.During the heating-up period,high melting TiO x particles which contains NbC with the size below 1μm can make a stronger pining force on the gain boundary migration than pure NbC ones,this effect restrain the austenite growth and control the austenite grain size to a certain extent.Then,when the cooling process begins,TiO x particles containing MnS with the size between 1 to 3μm act as a nucleation site for the intragranular acicular ferrite (IAF).Although the growth of bainite would extrude the IAF and make the smooth edge of IAF deformed,it still can not grow through the IAF.Just owing to the pining effect of TiO x-NbC particles and the hindering effect of IAF induced by the TiO x-MnS particles,prior austenite grains haven’t undergone a rapid growth during the heating process and these austenite grains are divided into small regions by the IAF finally.
