深过冷Cu40Co40Ti20合金的亚稳相分离与快速凝固

利用电磁悬浮技术和熔体快淬使Cu40Co40Ti20合金熔体达到深过冷,发生亚稳相分离.经悬浮冷却凝固的Cu40Co40Ti20发生液相分离,富Cu相中出现富(Co,Ti)相枝晶,富(Co,Ti)相中形成二次析出的富Cu相;经纯铜快淬处理的合金形成外层为富(Co,Ti)相,内部为富Cu相的双层球状结构.两种方法得到的组织中,富(Co,Ti)相内部均出现了二次析出的富Cu相小球.对样品进行X射线衍射分析,相组成主要有(Cu)和Co2 Ti相.     

深过冷条件下Cu—Co合金的二次液相分解与合金的凝固

采用熔融玻璃深过冷技术和金相分析法,对Cu-(10%-30%)Co合金液态深过冷条件下的二次液相分解和合金的凝固行为进行了分析,研究表明,由于液相分解后富C液相的溶解度随温度下降而降低,使Cu原子不断从富Cu原子不断从富C液相中分解出来,如果分解出的Cu原子不能扩散到富Cu原子不能扩散到富Cu液相中,会在富Co液相内形成富Cu液滴。但合金凝固后富Co相中富Cu相并非都来自于干净人液相分解,一部分是来自于富Co液相长大和富Co相选分结晶,冷却曲线的测定结果和分析显示,Cu-Co合金液相分解后,富Co液相的结晶温度与合金成分和实验条件有关,富Co液滴结晶完成后发生了包晶转变。     

Zr-Ce-Co-Cu难混溶合金的液-液相分离和双非晶相形成

在Zr-Ce二元稳态难混溶合金的基础上添加Co-Cu二元亚稳态难混溶合金,设计了四元(Zr_aCe_b)_(1-x)(Co_cCu_d)_x复合难混溶合金.通过热力学计算了Cu和Co在两分离液相中的分配系数,并利用OM,SEM,EDS,XRD和DTA等方法研究了相形成和组织演变的机制.结果表明,单一均匀的(Zr_aCe_b)_(1-x)(Co_cCu_d)_x合金熔体在凝固过程中发生液相分离,Co和Cu元素分别分布在富Zr和富Ce液相中,最终形成富Zr-Co和富Ce-Cu两液相.在快速凝固条件下,四元合金液-液分离形成的富Zr-Co和富Ce-Cu两液相分别发生玻璃转变,形成锆基和铈基两非晶相.实验研究与热力学分析相结合,揭示了Co与Cu原子比例和Co-Cu合金添加量以及冷却速率对双非晶相形成的影响,探索了由难混溶合金制备相分离非晶合金的方法.当Co与Cu原子比及添加量分别为4∶1和38.5%时,在熔体旋甩快速冷却条件下可以获得双相非晶合金.     

三元Fe62.5Cu27.5Sn10合金的快速凝固组织演变机制

在自由落体条件下研究三元Fe62.5Cu27.5Sn10合金的亚稳相分离和凝固组织形成规律。结果表明:液相分离使得合金液滴在快速凝固过程中形成2~3层壳核组织和均匀弥散组织,其相组成为α-Fe固溶体和Cu3Sn金属间化合物相。分析液滴内部L2(富Cu)液相的运动特征发现,温度梯度和浓度梯度所引起的Marangoni运动促进壳核组织的形成,合金液滴的最终凝固组织由冷却速率、过冷度和Marangoni运动共同决定。如果液滴直径足够小,快速冷却能够抑制液相分离,凝固组织演变为等轴枝晶形态,其相组成为α-Fe固溶体和Cu2FeSn化合物。EDS分析显示,初生α-Fe相在快速凝固过程中发生了显著的溶质截留效应。     

冷却速度对GH4710合金凝固过程偏析行为的影响

采用凝固重熔物理模拟实验,研究了不同冷速下GH4710合金凝固过程的元素偏析规律。结果表明,不同冷却速度下,GH4710合金中Ti元素的偏析程度最严重,Al、Co、Cr的偏析程度较低,当冷速超过3℃/min时,Al、Co、Cr的偏析系数受冷速变化的影响不明显。进一步的相图计算及微观分析表明,GH4710合金在非平衡凝固条件下,沉淀强化元素Al、Ti主要为正偏析元素,主要在枝晶间形成γ'相或γ/γ'共晶相,而合金中固溶强化元素Cr、Co元素在固相中富集,在液相中贫乏,具有典型的负偏析特征。GH4710合金元素的偏析行为主要取决于凝固过程的冷却速率及非平衡相变的综合作用。     

冷却条件对Fe_(77)Co_2Zr_9B_(10)Cu_2合金性能的影响

采用单辊快淬法制备Fe77Co2Zr9B10Cu2合金,并对该合金在600℃退火后,分别在炉内、空气和液氮中冷却,研究冷却条件对合金性能的影响。利用X射线衍射(XRD)和透射电镜(TEM)研究合金的微观结构;利用振动样品磁强计(VSM)测量合金的磁性能。结果表明,快淬态的Fe77Co2Zr9B10Cu2合金带含有α-Fe(Co)和H相。600℃退火后,在炉内冷却的合金中仅观察到α-Fe(Co)相,而经空气和液氮中冷却的合金中除α-Fe(Co)相仍然存在部分H相。600℃退火后,在炉内和空气中冷却后合金的磁性能相差不大。     

冷却速率对Zn-30Al-1Cu合金组织的影响

采用金相显微镜、扫描电镜、透射电镜和X射线衍射仪研究了冷却速率对Zn-30Al-1Cu合金微观组织的影响.结果表明,Zn-30Al-1Cu合金初始凝固组织主要由初生相α’相、包围在初生相周围的包晶β相和共析组织(α+η)组成,共析组织由包晶β相分解而来.凝固后期共析胞向枝晶中心生长,使α相分解为层片α+η组织.随冷却速率增大,初生相由枝晶状变成等轴晶粒,尺寸也越来越小,沉积态晶粒尺寸最细小,铸态晶粒尺寸最大.冷却速率提高Cu元素在基体相中的固溶度,沉积态合金中没有发现富铜相ε,Cu元素全部固溶到基体中;普通铸造和快速凝固合金中均发现富铜相ε,它们存在于枝晶间和η相中.     

冷却速度对CuCr25合金凝固过程的影响

研究了不同冷却速度下CuCr25合金的微观组织和凝固过程。随着冷却速度的增加，CuCr25合金的微观组织将变得越来越细。当冷却速度达到10^7K／s时，可获得纳米结构的微观组织。当冷却速度〈10^3K／s时，CuCr25合金的凝固过程为普通凝固过程：如果冷却速度〉10^4K／s，其凝固过程为液相分解凝固过程。在快速凝固过程中，CuCr25合金中没有新相形成。但是，Cu在富Cr相中和Cr在富Cu相中的溶解度有所增加。     

添加Cu-Nd的Mg2Ni型纳米晶和非晶合金的吸氢动力学性能（英文）

采用快淬方法制备添加Cu及Nd元素的具有纳米晶和非晶结构的(Mg24Ni10Cu2)100-x Nd x(x=0,5,10,15,20)合金。用X射线衍射(XRD)和高分辨率投射电镜(HRTEM)分析铸态及快淬态合金的相组成及结构,并研究Nd含量和快淬速率对合金相结构及吸氢性能的影响。结果表明,快淬态无Nd合金为纳米晶结构,而含Nd的快淬态合金则为纳米晶和非晶结构,表明添加Nd促进了合金的非晶形成能力。添加Nd及快淬处理均显著地促进了合金的气态及电化学动力学性能。添加Nd及快淬处理加快了氢原子在合金体内的扩散速率,但是均降低了合金电极表面的电荷传递性能,从而使得合金的高倍率放电性能(HRD)随着Nd含量和快淬速率的增加先上升而后下降。     

Ni对快速凝固Cu75Cr25合金相变及其凝固组织的影响

采用合金化的方法得到快速凝固Cu75-xCr25Nix(X=0.5,1和3) 合金的凝固组织.利用带有能谱(EDS)的扫描电子显微镜(SEM)分析了富Cr相的形态、成分以及形成机制.结果显示,合金元素Ni扩大了Cu、Cr之间的固溶度; Cu75Cr25合金快速凝固过程中的液相分解得到抑制.Cu75-xCr25Nix合金富Cr液相分解组织的数量、尺寸、形貌较Cu75Cr25合金富Cr液相分解组织均有较大的变化.在Cu75-xCr25Nix组织中发现,除富Cr液相分解组织之间有聚集现象以外,还存在富Cr液相分解组织与富Cr枝晶间的聚集.     

凝固速度对Ni47Ti44Nb9铸态合金组织和织构的影响

对比研究了Ni₄₇Ti₄₄Nb₉合金快冷铸锭和慢冷铸锭的宏、微观组织和织构特点,分析了凝固速度对组织和织构的影响机理。采用光学显微镜(OM)和扫描电子显微镜(SEM)观察了微观组织,采用X射线衍射(XRD)分析了织构。结果表明,铸态Ni₄₇Ti₄₄Nb₉合金具有<113>方向的择优生长取向;凝固速度对Ni₄₇Ti₄₄Nb₉合金铸态组织和织构的形成具有重要影响,快速冷却条件下获得均匀的树枝晶组织,铸锭的横、纵截面均形成{113}织构,慢速冷却条件下形成具有特定方向的柱状树枝晶,纵截面织构以{113}<361>、{113}<332>和{113}<141>为主;凝固过程中热量方向性传导造成的树枝晶定向生长是影响合金铸态组织和织构形成的主要原因。     

The metastable liquid miscibility gap in Cu-Co-Fe alloys

The metastable liquid-phase separation (MLPS) in the Cu-Co-Fe system was investigated using an electromagnetic levitation melting and solidification technique. It was found that when ternary alloys containing more than 10wt.% (12 at.%)Co and 10wt.% (11at.%)Fe were undercooled below a certain temperature, T _sep, the homogeneous melt separated into two liquid phases. In alloys containing more than 54 to 57wt.% (49 to 54at.%)Cu (depending on the Co and Fe content), the phase separation generally appeared as dispersed (Fe, Co)-rich droplets (L₁) in a Cu-rich matrix, whereas for alloys containing less copper, the separation resulted in Cu-rich droplets (L₂) in a (Fe, Co)-rich matrix. The metastable liquid miscibility gap boundary of the Cu-Co-Fe ternary was determined using the measured T _sep and the composition of the separated phases. The ternary liquid-phase separated boundaries were found to be consistent with a cross-sectioned phase diagram in which one axis represents pure copper and the other Fe + Co.     

The metastable liquid miscibility gap in Cu-Co-Fe alloys

The metastable liquid-phase separation (MLPS) in the Cu-Co-Fe system was investigated using an electromagnetic levitation melting and solidification technique. It was found that when ternary alloys containing more than 10wt.% (12 at.%)Co and 10wt.% (11at.%)Fe were undercooled below a certain temperature, T _sep, the homogeneous melt separated into two liquid phases. In alloys containing more than 54 to 57wt.% (49 to 54at.%)Cu (depending on the Co and Fe content), the phase separation generally appeared as dispersed (Fe, Co)-rich droplets (L₁) in a Cu-rich matrix, whereas for alloys containing less copper, the separation resulted in Cu-rich droplets (L₂) in a (Fe, Co)-rich matrix. The metastable liquid miscibility gap boundary of the Cu-Co-Fe ternary was determined using the measured T _sep and the composition of the separated phases. The ternary liquid-phase separated boundaries were found to be consistent with a cross-sectioned phase diagram in which one axis represents pure copper and the other Fe + Co.     

Annealing effects on the microstructure and properties of bulk high-entropy CoCrFeNiTi0.5 alloy casting ingot

Most previous researches focused on small casting ingots prepared by arc melting, when studying high-entropy alloys. Large sized ingots were also necessary in exploring the existence of volume effects in the multi-principal element alloys. During the experiments, a large sized CoCrFeNiTi_0.5 alloy casting ingot was prepared by a medium frequency induction melting furnace. A slight volume effect occurred, reflecting mainly in the growth of crystalline grains and the increase of alloy hardness in the ingot. To investigate the effect of annealing temperature on microstructure and properties of CoCrFeNiTi_0.5 alloy, several samples taken from the ingot were annealed at 600 °C, 700 °C, 800 °C and 1000 °C respectively for 6 h. Almost no effects were found to the crystalline structure and elemental distribution when the samples were annealed below 1000 °C. The crystalline structure of CoCrFeNiTi_0.5 alloy was composed of one principal face-centered cubic (FCC) solid-solution matrix and a few intermetallic phases in the form of interdentrite. Dendrite contained approximately equivalent amount of Co, Cr, Fe, Ni and a smaller amount of Ti. When annealed below 1000 °C, the interdendrite stayed in (Ni, Ti)-rich phase, (Fe, Cr)-rich phase and (Co, Ti)-rich phase. After 1000 °C annealing, (Co, Ti)-rich phase disappeared, while (Ni, Ti)-rich phase and (Fe, Cr)-rich phase grew. The microhardness of the as-cast CoCrFeNiTi_0.5 alloy was 616.80 HV and the macrohardness was 52 HRC. The hardness of the samples stayed generally unchanged after annealing. This indicated a high microstructure stability and excellent resistance to temper softening that the CoCrFeNiTi_0.5 alloy exhibited.     

冷喷涂辅助原位合成FeCoxCrAlCu高熵合金涂层组织性能研究

利用冷喷涂辅助原位合成高熵合金涂层的方法,在45_^#钢基体表面成功制备出不同Co含量的FeCo_xCrAlCu(x=0,0.5,1,1.5,2)高熵合金涂层。通过XRD、SEM、EDS、TEM、显微硬度计、磨料磨损试验机、电化学工作站等设备,检测分析了Co含量的变化对合金涂层相结构、显微组织,硬度、耐磨性及耐腐蚀性的影响。结果表明：合金涂层是由简单的FCC+BCC双相混合结构组成,Co含量的改变对涂层相组织的数量影响不大;随着Co含量的增加,合金涂层中显微组织的枝晶数目增加,并且得到明显粗化,通过面扫得显微组织中枝晶内富集Fe,Cr,Co元素,枝晶间富集Cu元素,Al均匀的分布在整个涂层中;随着Co含量的增加,硬度先增加后减小,在Co=1时合金涂层硬度达到最大为555.6HV;合金涂层中最小的摩擦系数为0.361;在3.5wt.%NaCl腐蚀介质中,合金涂层相比与45_^#钢基体具有较正的自腐蚀电位(E_corr=-0.325V),说明涂层耐腐蚀性比基体好。     

Microstructure evolution of Al0.6CoCrFeNi high entropy alloy powder prepared by high pressure gas atomization

The influence of cooling rate on the microstructure of Al_0.6CoCrFeNi high entropy alloy (HEA) powders was investigated. The spherical HEA powders (D₅₀≈78.65 μm) were prepared by high pressure gas atomization. The different cooling rates were achieved by adjusting the powder diameter. Based on the solidification model, the relationship between the cooling rate and the powder diameter was developed. The FCC phase gradually disappears as particle size decreases. Further analysis reveals that the phase structure gradually changes from FCC+BCC dual-phase to a single BCC phase with the increase of the cooling rate. The microstructure evolves from planar crystal to equiaxed grain with the cooling rate increasing from 3.19×10⁴ to 1.11×10⁶ K/s.     

储氚合金ZrCo0.8M0.2 (M = Co, Cu, Cr, Mn, Al)的性能研究

采用电弧熔炼的方法在氩气气氛中熔炼了ZrCo_0.8M_0.2 (M = Co、Cu、Cr、Mn、Al)合金。合金的主相均为ZrCo相,但Cr、Mn和Al部分替代Co后形成了第二相。Cr替代形成了Zr₂Co和ZrCr₂相,Mn替代形成了Zr₂Co和ZrMn₂相,Al替代形成Zr₃Co和Zr₆CoAl₂相。Cr和Mn的替代使合金的晶胞体积减小,而Cu和Al的替代使晶胞体积增大。Cu、Cr、Mn和Al替代后,ZrCo_0.8M_0.2合金的平台压变化不明显,但吸氢量出现了不同程度的降低。Cr和Mn元素的替代明显改善了ZrCo合金在室温下的活化性能。Cr和Mn元素的替代降低了高温下ZrCo合金发生歧化反应的速率,这主要是由于Cr和Mn元素的掺杂减少了氢原子占据不稳定位置8f₂ 和8e的数量,从而降低了歧化反应发生的驱动力。     

Rapid solidification of Cu84Co16 alloy undercooled into the metastable miscibility gap under different conditions

The Cu₈₄Co₁₆ alloy melt processed by differential thermal analysis, electromagnetic levitation and drop tube experiences a liquid phase separation when it is undercooled into the metastable miscibility gap. The phase separation and coagulation processes are mainly controlled by the degree of undercooling, cooling rate and convection level in the containerless states. Disperse structures have been formed in droplets solidified during free fall in the drop tube.     

Effect of cooling rate on solidification microstructure and mechanical properties of TiB2-containing TiAl alloy

Effects of cooling rate and 0.25 at.% TiB₂ addition on solidification microstructure and mechanical properties of Ti–48Al–2Cr–2Nb alloys fabricated by the investment casting with different thicknesses were studied. The results show that with the cooling rate increasing from 37 to 2×10² K/s, the solidification path of the studied alloys is unchanged. The grain size of the matrix alloy is refined from 650 to 300 μm, while the grain size of Ti–48Al– 2Cr–2Nb–TiB₂ is reduced from 550 to 80 μm. The lamellar spacing of matrix alloy is reduced from 360 to 30 nm with increasing the cooling rate from 37 to 2×10² K/s, while TiB₂ addition shows little refinement effect on the lamellar spacing. Ti–48Al–2Cr–2Nb–TiB₂ sample under medium cooling rate (69 K/s) exhibits superior microhardness (HV 550) and ultimate tensile strength (570 MPa) among the studied alloys. The refined grain size, lamellar spacing and fine TiB₂ particles could account for the favorable mechanical properties of the studied TiB₂-containing alloy. The microstructure evolution was discussed in light of cooling rate, constitutional supercooling and borides addition.