稀土在Al-Ti-B-RE细化剂中的作用及细化机理研究

采用纯钛颗粒熔铸法制备Al-Ti-B-RE细化剂,并就稀土在Al-Ti-B-RE细化剂中的作用及细化机理进行了研究。结果表明:稀土元素加入后,增强了铝液对TiAl3、TiB2相的润湿性及异质形核能力,延缓细化剂的衰退时间;不同细化剂的细化效果主要取决于形核相TiAl3和TiB2粒子的特性,其中以TiAl3相的形貌、尺寸和数量影响较大,含有大量细小、弥散分布的块状TiAl3相的细化剂表现出良好的细化效果,而TiB2相成为影响α-Al有效形核数的主要因素,Al-Ti-B-RE细化剂的细化效果及抗衰退性优于进口或国产Al-Ti-B细化剂。     

掺杂Si-Al-K对钼粉及其烧结制品组织、性能的影响

研究了不同含量掺杂元素对钼粉形貌、烧结坯及钼丝微观组织的影响。研究表明，随着掺杂元素含量的升高，钼粉粒度逐步细化：在烧结过程中，掺杂元素在烧结坯形成非晶相的第二相粒子，并且随着掺杂元素含量的升高，第二相粒子的分布密度增大，使烧结坯晶粒得到细化；在加工过程中，烧结坯中的第二相粒子碎化为粒子串，粒子串分布于纤维晶界处，可改善钼丝性能。     

超细第二相粒子强化钢铁材料的研究进展

 综述了钢中有关第二相粒子的研究进展情况，分析了第二相粒子对钢强韧性能的影响及第二相粒子细化钢晶粒的基本理论，概括了获得超细第二相粒子的基本方法，指出了存在的问题并提出了获得超细第二相粒子的新思路。     

重熔保温时间对Al-Ti-C中间合金微观组织及细化性能的影响

利用Al、Ti、C粉末原料,采用铝熔体热爆法合成了相同成分不同微观组织形貌的两种Al-Ti-C中间合金晶粒细化剂。借助X射线衍射(XRD)、大型光学显微镜(MEF3)等分析手段研究了重熔保温时间对Al-Ti-C中间合金微观组织及细化效果的影响。结果表明:合成的两种Al-Ti-C中间合金均由Al、TiAl3和TiC组成。重熔时,保温时间对Al-Ti-C中间合金微观组织产生重要影响。随着重熔保温时间的延长,TiAl3会发生聚集、长大,而TiC颗粒有聚集倾向,但保温过程中,TiAl3和TiC相表现出较强的稳定性,并没有生成其他杂相如Al4C3等。重熔后的Al-Ti-C中间合金仍具有一定的晶粒细化能力。     

钙镁复合变质剂对冷轧高强钢组织遗传性及塑性影响

利用光学显微镜(OM)、透射电镜(TEM)和电子背散射衍射(EBSD)等设备研究了Ca-Mg复合变质剂对冷轧超高强钢铸坯中TiN粒子析出的影响机制,并对显微组织在各工序的遗传性及塑性改善进行了系统对比。结果发现:添加变质剂以后,铸坯中TiN第二相粒子尺寸明显变小,数量增多,分布更弥散;添加改质剂后钢坯、热轧钢板中沿晶界铁素体减少,冷轧退火后显微组织变细;与未添加变质剂试验钢比,屈服强度和屈强比提高,材料折弯、扩孔率得到改善。变质剂的添加改变了钢液中TiN形核机制。弥散的TiN可以细化铸态组织,并通过遗传效应对热轧、冷轧连退组织产生影响,改善力学性能和成型性能。     

成品退火温度对Zr-Nb合金棒材组织与织构的影响

通过金相组织观察、第二相粒子观察及织构分析,研究成品退火温度对Zr-Nb合金棒材组织与织构的影响。结果表明:随着成品退火温度的升高,Zr-Nb合金棒材金相组织中晶粒逐渐增大,第二相粒子的平均尺寸和尺寸分布范围均逐渐增大。各种退火温度下的Zr-Nb棒材均存在{0002}基面织构,且不同退火温度的棒材织构强度差别较为明显。     

B/Zr摩尔比对Al-Zr-B合金的组织和晶粒细化效果的影响

以Al,K2ZrF6和KBF4为原料,采用熔体反应法制备不同B/Zr摩尔比Al-Zr-B合金。利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射分析(XRD)等手段研究了B/Zr摩尔比对Al-Zr-B中间合金的组织和晶粒细化效果的影响。结果表明,随着B/Zr摩尔比的增加,Al-Zr-B中间合金的第二相组成发生改变。当B/Zr摩尔比为1时,第二相主要由粗大的块状ZrAl3相及少量团聚在晶界上的ZrB2粒子组成;当B/Zr摩尔比为2时,第二相为ZrB2粒子和少量块状ZrAl3相。当B/Zr摩尔比为3时,第二相全部为ZrB2粒子。对AZ91D合金的细化实验表明,随着B/Zr摩尔比的增加,晶粒细化效果越好,添加B/Zr摩尔比为3的Al-Zr-B中间合金具有明显的细化效果,合金由粗大的树枝晶转变成细小的等轴晶,固溶处理后的AZ91D合金平均晶粒尺寸由约328μm下降到约120μm;抗拉强度和延伸率达到213 MPa和4.95%,比未添加细化剂时分别提高了15.1%和30.3%。晶粒细化机制可归结为ZrB2粒子作为α-Mg的异质形核核心。     

α相含量对AA3104铝合金热轧组织及退火行为的影响

通过对AA3104铝合金均匀化时间的控制,获得α相含量分别为18%和68%的初始材料,并对其进行轧制温度约为480℃~420℃、形变量为95%的热轧形变。利用扫描电镜(SEM)及能谱仪(EDS)对第二相含量、平均尺寸以及尺寸分布进行定量表征。利用显微硬度测定了不同α相含量热轧板的再结晶温度,利用X射线衍射技术(XRD)对再结晶前后织构进行研究,并对比分析织构差异。结果表明:热轧后,α相含量为18%的第二相粒子中尺寸接近5μm的粒子数量较少,其完全再结晶温度约为380℃,且立方织构的含量低;α相含量为68%的试样热轧后含有更多尺寸接近5μm的第二相粒子,其完全再结晶温度约为340℃,且立方织构含量较前者高,结果表明含有第二相粒子的AA3104铝合金热轧组织及退火行为与α相含量有关。     

不同钛碳比制备的Al-TiO_2-C细化剂对ZL101细化变质效果研究

以纳米TiO_2粉、C粉和Al粉为原料,利用放热弥散法原位合成含有Al_3Ti,TiC和Al_2O_3相的Al-TiO_2-C细化剂,钛和碳的摩尔比分别为1∶1,3∶1,5∶1,8∶1,10∶1和15∶1,研究不同钛碳比制备的细化剂对ZL101合金细化变质效果的影响。利用X射线衍射仪(XRD)、扫描电镜(SEM)及能谱仪(EDS)研究钛碳比对Al-TiO_2-C细化剂相组成和显微组织的影响。将制备好的Al-TiO_2-C细化剂加入到ZL101合金中进行细化变质实验,利用MATLAB软件提取冷却曲线的特征值评价细化变质效果。结果表明:钛碳比为10∶1时,Al-TiO_2-C细化剂组织中Al_3Ti呈圆块状且数量最多,尺寸均匀,TiC颗粒和Al_2O_3颗粒在晶界弥散分布,取质量分数为0.3%的此种组织的细化剂细化变质ZL101合金后,初晶最低过冷温度T_(min)=586.8℃,初晶再辉温度ΔT_1=0.4℃均达到最小,证明细化效果最好,细化后平均晶粒尺寸为71.6μm;变质前后共晶生长温度之差ΔT_E=14.4℃达到最大,变质效果理想。因此,钛碳比为10∶1时制备的细化剂对ZL101合金具有最好的细化变质效果。     

稀土Nd对铸造铝硅合金变质作用的长效性及重熔性研究

以稀土元素Nd为变质剂,采用金属型铸造工艺制备铸造铝硅合金ZL101,并通过金相显微镜、扫描电镜、布氏硬度计和电子万能试验机研究变质时间及重熔次数对合金显微组织和力学性能的影响.结果表明,稀土Nd对合金具有较好的变质作用,并具有长效性和重熔性,变质6h及重熔4次后合金中的共晶硅组织仍呈小片状的变质状态,且合金硬度及拉伸性能均未受明显影响.变质不同时间及重熔不同次数的合金拉伸试样均为解理断裂.     

低碳微合金钢中Nb、Ti碳氮化物的回溶行为研究

利用透射电镜和X射线衍射技术研究了一种低碳微合金钢中Nb、Ti碳氮化物的回溶行为.研究结果表明,随着加热温度的升高,保温时间的延长,第二相粒子发生回溶,第二相粒子的数量减少,尺寸也逐渐变细小.同时,粒子形貌由主要呈近球形逐渐变为主要呈方形.加热过程中,Nb和Ti的碳氮化物均会发生溶解,Nb的回溶速度要比Ti快.     

Effects of second-phase particles on coarsening of austenite in 0.15 Pct carbon steels

The effects of second-phase particles formed by the addition of vanadium, nitrogen, and aluminum on the austenite grain coarsening behavior of 0.15 pct carbon steels were studied. The oxidation and etching technique has been adopted to reveal the prior austenite grain boundaries. The specimens were austenitized at intervals of 50°C within the range of 900°C to 1150°C under high vacuum (<10⁻⁴ torr) for half an hour, toward the end of which they were oxidized for about one minute by introducing oxygen at about 250 mm Hg to reveal the grain boundaries, and then quenched into iced water. The variation of prior austenite grain size with temperature in these steels indicates that vanadium carbonitride, V(C, N), is much more effective in austenite grain refinement than vanadium carbide, VC, at all temperatures. The effect of vanadium carbonitride in austenite grain refinement is more or less the same as that of aluminum nitride. AlN, at temepratures below 1000°C, but this effect of vanadium carbonitride in austenite grain refinement decreases with increasing temperature. Above 1000°C, aluminum nitride is a much better grain refiner than vanadium carbonitride. The presence of the V (C, N) and AlN particles in the same steel causes moderate grain growth of austenite. MD. Mohar Ali Bepari, formerly with the Department of Metallurgy, The University of Sheffield, Sheffield, England, is Associate Professor of Department of Metallurgical Engineering, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh.     

电磁搅拌对A1-5Ti-1B的显微组织与晶粒细化能力的影响

在中间包对A1-5Ti-1B熔体施加电磁搅拌,然后连续铸挤成A1-5Ti-1B丝,研究了电磁搅拌对A1-5Ti-1B的显微组织与晶粒细化能力的影响,结果表明：电磁搅拌能够阻止TiB2粒子的团聚和沉淀,改善TiB2粒子的分布均匀性,提高A1-5Ti-1B的晶粒细化能力．A1-Ti1B的Ti、B元素含量分别为5．08％和1．02％,TiB2粒子平均尺寸为0．74μm,TiAl3相平均尺寸为15．7μm．添加0．2％的AI-5Ti-1B后保温2min,可使纯铝晶粒从2800μm细化至68μm,保温120min,晶粒未见长大．     

Study of the mechanism of grain refinement of aluminum after additions of Ti- and B-containing master alloys

A highly sensitive thermal analysis technique has been used to study the mechanisms of grain refinement in high-purity aluminum. Additions of Al-Ti-B master alloys were made both below and above the peritectic concentration in reference to the Al-rich corner of the binary Al-Ti phase diagram (0.15 pct Ti in solution). The experiments were conducted at various times after the addition of grain refiner. From the results, except for formation of TiB₂, no effect of boron on the Al-rich portion of the binary Al-Ti phase diagram can be observed. With hypoperitectic additions of Al-Ti-B master alloys, TiB₂ particles are the most frequent nucleant for aluminum grains. Also, when Al-5Ti-lB additions are made, nucleation frequently occurs above the equilibrium liquidus temperature. From a thermodynamic point of view, this phenomenon can occur only if regions of the melt (which contain bondes and nucleate new grains) have a higher Ti concentration than is present in the bulk of the liquid. A mechanism has been proposed to account for this observation. When hyperperitectic additions of grain refiner were made, a metastable formation of Al solid was often observed to occur at 2 to 5 deg above the equilibrium peritectic temperature. Other researchers have made this observation and proposed that a metastable aluminide phase was formed, even though no X-ray evidence of this phase was found. The experiments reported here show that the metastable nucleation occurs on boride particles when cooling from high temperature, which allow high (metastable) quantities of dissolved Ti to be retained in portions of the melt.     

Microstructure and refining performance of an Al-5Ti-0.25C refiner before and after equal-channel angular pressing

Refining experiments were conducted to evaluate the grain refining performance of an Al-5Ti-0.25C refiner before and after equal-channel angular pressing (ECAP) with the use of a high-purity Al. The results show that the Al-5Ti-0.25C refiner has remarkable and stable grain refining performance when the holding times are within 5 to 30 minutes and the melt temperatures are within 1003 to 1073 K. Furthermore, some Al-5Ti-0.25C refiner samples were subjected to severe plastic deformation by using the ECAP technique at 298 K. It was found that Al₃Ti and TiC particles were significantly fragmented and their mean sizes were decreased to 10 and 1.08 μm, respectively, and the Al-5Ti-0.25C refiner appeared to have a double grain refining effect in comparison with that of before ECAP. It is also testified that the Vickers microhardness (Hv) value of the pure Al samples refined by the Al-5Ti-0.25C refiner after ECAP processing has a significant increment than that of before ECAP processing. It is concluded that the Al-5Ti-0.25C refiner with ECAP technique has a very useful practical application in refining industrial Al alloys.     

船板钢不同N含量第二相粒子变化规律

利用萃取复型和焊接热模拟技术,对不同N含量的EH36船板钢第二相粒子的形态、尺寸及分布情况进行了分析。结果表明,高N含量钢中的第二相粒子数量多于低N含量钢,并且粒子分布更加弥散。热模拟时间为50 s时,粒子在热循环过程中以小粒子的消失为主要特征,150 s时,粒子不仅发生溶解和长大,在钢中还出现了独立形核的第二相粒子。     

Effect of La on Microstructure and Grain-Refining Performance of Al-Ti- C Grain Refiner

Al-Ti-C grain refiner was prepared by SHS （self-propagating high-temperature synthesis ）-melting technique. The effect of La on the microstructures of grain refiner was studied by OM, TEM, SEM, XRD, and EDS. The experimental results indicate that La can improve the wettability between liquid aluminum and graphite ; the addition of La results in dispersive distribution of TiAl3 and TiC particles in the matrix. An excellent grain refining performance of Al-Ti-C grain refiner on commercially pure Al was obtained.     

Influence of Gadolinium with Small Content on Recrystallization Behaviour inSilver-Gold Alloys

Ag-Aualloyisatypicalis0morphousbinnyalloysystem.TheeffectofAucontent(<5%)inAg-Aualloysonrecrystallizati0ntemperaturehasbeenstudiedinRef.[1].Itwasf0undthatoftherelationshipwasdifferentfr0mthat0ftheCucofitentonrecrystallizati0ntemperatureinAg-Cualloyswhichisalindteds0lublealloysys-t..'2].InRefs.[3]and[41theinfluenceofsmal1additi0n0fGdandSm0ntherecrysta]iIza-tionbehavi0r0fAg-Cu.alloyshasbeenstudied,respectively.InthispaPertheresultsab0uttheialluence0fsmallGdadditi0nontherecrystal-lizationb…     

Microstructure and refining performance of an Al−5Ti−0.25C refiner before and after equal-channel angular pressing

Refining experiments were conducted to evaluate the grain refining performance of an Al−5Ti−0.25C refiner before and after equal-channel angular pressing (ECAP) with the use of a high-purity Al. The results show that the Al−5Ti−0.25C refiner has remarkable and stable grain refining performance when the holding times are within 5 to 30 minutes and the melt temperatures are within 1003 to 1073 K. Furthermore, some Al−5Ti−0.25C refiner samples were subjected to severe plastic deformation by using the ECAP technique at 298 K. It was found that Al₃Ti and TiC particles were significantly fragmented and their mean sizes were decreased to 10 and 1.08 μm, respectively, and the Al−5Ti−0.25C refiner appeared to have a double grain refining effect in comparison with that of before ECAP. It is also testified that the Vickers microhardness (Hv) value of the pure Al samples refined by the Al−5Ti−0.25C refiner after ECAP processing has a significant increment than that of before ECAP processing. It is concluded that the Al−5Ti−0.25C refiner with ECAP technique has a very useful practical application in refining industrial Al alloys. ZUOGUI ZHANG, formerly Master's Student, the Key Laboratory of Liquid Structure and Heredity of Material, Ministry of Education, Shandong University, Jinan 250061, People's Republic of China     

Structural Morphologies and Deformaiton Characteristics of Semi‐solid Type 304 Stainless Steel during Solidificaiton and Remelting

Microstructural evolutions of type 304 stainless steel and the related mechanical property of flow stress in semi‐solid state are investigated. The evolutions of microstructure during solidification, partial remelting of a hot‐rolled billet and partial remelting of a cast billet are compared with respect to structural morphologies in the semi‐solid state. Various structural morphologies, such as the linear and multilayered liquid/austenite/δ‐ferrite structure, globular liquid/δ‐ferrite structure and dendrite structure, are characterized using optical micrographs and an EPMA (electron probe microanalyzer). The various structural morphologies in the semi‐solid state are influenced not only by the phase transformation but also by the previous treatment of type 304 steel, such as hot rolling and casting. Furthermore, a series of hot compression tests are conducted for various combinations of deformation rate and deformation temperature in the semi‐solid state, to measure the flow stress and the change in microstructure resulting from plastic deformation. Flow stress, phase segregation, microfracture and distortion of solid particles during and after the hot compression test are strongly affected by the structural morphology in the semi‐solid state, such as the dendrite structure, nonglobular structure and globular structure. Semi‐solid type 304 stainless steel with dendrite structure exhibits the highest flow stress, which is about three times that of steel with globular structure, although the testing temperature and deformation rate are controlled to be the same. This is a result of the higher bonding force between solid particles and lower fluidity of the liquid phase of the dendrite structure than those of the globular structure, which exhibits excellent fluidity of the liquid phase and rotation of solid particles.