Ti对Fe-Ni膨胀合金凝固组织的影响

采用变质处理法和扫描电镜(SEM)研究了Ti对Fe-Ni膨胀合金凝固组织的影响.结果表明:经Ti变质处理后,Fe-Ni膨胀合金中形成了大量的Ti2O3-MnS高熔点复合夹杂物,尺寸约为2μm;Ti2O3复合夹杂物在凝固过程中作为非自发形核核心,使铸坯凝固组织细化.Ti在凝固组织的等轴晶和柱状晶晶界上以TiN,TiC,Ti(NC),Ti2O3形式存在,在一定程度上起到阻止晶粒长大的作用.     

含Ce2O3氧化物对改善双相不锈钢亚稳态点蚀的机理研究

利用扫描电镜、原子力显微镜、恒电位脉冲等研究了2205双相不锈钢在中性含Cl-环境下氧化物引起点蚀萌生的机理。实验发现MgO-Al_2O_3系夹杂物中MgO偏聚处以及MgO-Al_2O_3-CaO系夹杂物中CaO富集处会引起夹杂物处基体同周围基体接触电势差增加。此外,CaO富集处易使夹杂物表面出现显微缝隙并使基体裸露,产生亚稳态蚀坑。经Ce处理后发现夹杂物成分变为含Ce_2O_3·11Al_2O_3或Ce_2O_3·Al_2O_3为主的复合夹杂,夹杂物与基体接触电势差减小并且在含Ce_2O_3复合夹杂物处未发现点蚀萌生现象,最后阐述了非金属氧化物引起点蚀的机理以及Ce与氧化物反应的机制。     

微镁处理对铸态低碳钢中夹杂物和组织的影响

在实验室条件下,对低碳钢进行微镁处理,以SEM-EDS和金相显微镜为表征手段,通过与空白样的对比,研究钢中夹杂物、组织的演变过程。结果表明:微镁处理使得夹杂物从Al_2O_3转变为Mg-Al-O复合夹杂物,并且其尺寸明显细化,密度显著增加。组织分析表明:Mg-Al复合夹杂物能够诱导晶内针状铁素体形核,并且在这些夹杂物附近的铁基体中存在贫锰区。理论分析认为这促进了晶内针状铁素体的形核,结晶核心起源于复合夹杂物中镁铝尖晶石的镁空位。     

700 ℃超超临界锅炉材料GH4700镍基合金Al2O3+TiN复合析出行为研究

运用金相、扫描、热力学与动力学计算的方法,对真空感应冶炼GH4700镍基高温合金中Al2O3+TiN复合析出行为进行研究,结果表明:Ti、N、O的偏析因子对冷速不敏感;合金中以Al2O3+TiN复合夹杂为主;纯TiN只能在固相分数大于95%的两相区开始生成,尺寸约为4.5～5μm,与实际观察的尺寸基本吻合,而对于Al2O3+TiN复合夹杂物,尺寸及分布范围较纯TiN析出物要宽.     

添加Ti对Fe-4％Si合金凝固组织的影响及机理

选用能将初生δ-铁素体保留至室温的Fe-4％Si合金,通过对比添加Ti与不加Ti的合金铸锭的宏观组织,研究添加Ti对Fe-4％Si合金凝固组织的细化作用.采用SEM+EDS对含Ti合金中Ti化合物相进行观察表征,并利用EBSD结合能谱分析对其进行相鉴定.利用边-边匹配(E2EM)模型计算TiN与δ-Fe之间的原子匹配错配度,预测两者之间的位向关系,从晶体学角度探讨TiN对δ-Fe异质形核的效用,并分析Ti的溶质作用.结果表明,添加0.065％Ti使Fe-4％Si合金凝固组织中的柱状晶全部变为等轴晶,添加Ti原位形成的TiN能够作为Fe-4％Si合金凝固时δ-铁素体异质形核的有效核心,TiN的异质形核作用及Ti的溶质作用使柱状晶全部变为等轴晶,有效细化了Fe-4％Si合金的凝固组织.     

纳米晶体Fe2O3点阵参量的研究

对γ相和α相纳米晶体Fe_2O_3的系列样品进行了X射线衍射点阵参量实验研究和计算。结合所得到的晶粒度和微结构参数，发现纳米晶体Fe_2O_3的晶粒组元中存在着晶格畸变；随着温度的升高，γ相和α相纳米晶体Fe_2O_3的点阵参量呈现出了明显的变化，其晶格畸变与晶粒度和温度有较密切的关联。     

氮在浆体输送管线用钢中的作用和行为

研究了氮在浆体输送管线用钢中的作用和行为.钢中加入0.007-0.02%N和相应数量的Ti,以保证TiN从奥氏体中析出,但不从液相中析出.充分利用固溶氮的固溶强化作用和析出氮化物对铁素体晶粒尺寸细化和促进高韧性针状铁素体的形成的有利作用.两者的有效结合使钢获得了良好强韧性配合及耐腐蚀性能.     

双相不锈钢F55电渣重熔过程夹杂物的控制

本文重点研究了双相不锈钢F55的电渣重熔工艺,研究发现,F55电极经过电渣重熔后钢中氧含量增加,经扫描电镜检测分析,钢中的夹杂物类型主要为高熔点的Al_2O_3。通过优化电渣工艺,采用CaF_2-CaO-Al_2O_3-MgO-SiO_2五元渣系,同时渣中加SiCa、Al对熔渣进行脱氧,Al_2O_3夹杂物发生变性,形成低熔点复合夹杂物,易于从钢中去除,从而实现F55电渣过程夹杂物的有效控制。     

原位金属间化合物增强铝基复合材料研究

(1)成功制备出了增强相Al_3Ti尺寸小于0.5μm、AlN的尺寸达到纳米的AlN.Al_3Ti/ZL101原位复合材料。增强相Al_3T_i的尺寸大小取决于制备工艺及合金液中T_1元素的扩散速度。Al_3Ti晶核形成后对其周围溶质的吸附作用满足Langmuir吸附理论。吸附的溶质阻碍了Ti元素的扩散,使Al_3Ti晶核形成后很难长大而能大量形核,并保持亚微米级尺寸。采用X射线衍射及TEM方法分析并确定了增强相Al_3Ti和AlN。(2)二水平七因素及三水平四因素正交实验确定了AlN.Al_3Ti/ZL101原位复合材料的最佳成分。该原位复位材料的最大拉伸强度为360MPa、布氏硬度为122、弹性模量达到92GPa、延伸率为3.8％。(3)原位复合材料晶粒尺寸较基体细小得多。Al_3Ti可显著细化α-Al晶粒,α-Al晶粒的细化使其周围的共晶硅细化;AlN相存在于共晶硅中,作为异质晶核可显著细化共晶硅。TEM分析表明,基体和增强相Al_3Ti之间存在一定的晶体学位向关系并出现共格现象。原位复合材料的主要强化机制为细化晶粒强化(细化α-Al晶粒、细化和粒化共晶硅晶粒、细化AlN晶粒和细化Al_3Ti晶粒)、弥散强化和复合强化。(4)首次研究了原位复合材料的铸造性能和重复使用性能。在铝合金铸件的正常浇注温度下,AlN.Al_3Ti/ZL101原位复合材料有较基体ZL101更好的流动性、更小的     

钒-钛微合金化钢焊接热影响区晶内铁素体与夹杂物的界面关系

采用聚焦离子束方法制备试样,利用最高加速电压为1 300 kV的高分辨电镜观察钒-钛微合金化钢100 kJ/cm大线能量热模拟焊接热影响区,对作为晶内铁素体形核核心的夹杂物形貌与结构及夹杂物与晶内铁素体界面关系进行了研究.结果表明,晶内铁素体在MnS V(C,N)复合夹杂物相上形核析出,夹杂物和晶内铁素体存在确定的晶体学位向关系.     

Mechanisms of inclusion formation in low alloy steels deoxidised with titanium

Abstract

In the present investigation, the conditions for inclusion formation in two Ti deoxidised steels and one Al–Ca deoxidised steel have been examined by means of optical and electron microscopy, in combination with a thermo dynamic analysis of the phase relations involved. It is concluded that the Ti containing inclusions form as a result of a series of reactions occurring in the ladle, during solidification and in the solid state. The important solid state reaction products are MnS, TiN, and MnOTiO₂ . The presence of Mn rich compounds at the surface of the inclusions is consistent with the observation of a Mn depleted zone in the surrounding steel matrix. In contrast, the primary inclusions in the Al–Ca deoxidised steel are complex oxysulphides, which are thermodynamically more stable and can therefore form in the liquid state.     

Optimising inclusion and toughening the heat-affected zone of ship plate steel with MgO nanoparticles

The effect of adding MgO nanoparticles to ship plate steel at welding heat-affected zones (HAZs) was experimentally studied. The results showed that the added nanoparticles obviously optimised the inclusions; the average size of the inclusions was significantly reduced, and the distribution was relatively uniform. The toughness of the base metal and HAZ increased by 20–60 J, apart from a slight decrease in the strength of the fine-grained heat-affected zone and a nearly unchanged strength in the coarse-grained heat-affected zone, and approximately ～2?μm (Mg–Al–Ti)O-containing inclusions induced acicular ferrite effectively, thereby simultaneously enhancing the strength and toughness of the inter-critical heat-affected zone. In conclusion, these performance improvements in both the base metal and HAZ could be attributed to grain refinement and inclusion optimisation.     

Nature of inclusions in steel weld metals and their influence on formation of acicular ferrite

Abstract

The chemistry and structure of weld metal inclusions has been studied. Four submerged arc welds which utilized plate and consumables to cover a range of oxygen and deoxidant contents were examined. Analysis of the inclusions was carried out on carbon extraction replicas in a Philips 400T scanning transmission electron microscope, fitted with an energy dispersive analyser. Two major types of inclusion were found. With weld metal aluminium approaching the stoichiometric ratio with oxygen, the inclusions were crystalline and had a spinel structure at the centre with a discontinuous, polycrystalline, titanium-rich phase on the surface. With weld metal oxygen high compared with the stoichiometric ratio with aluminium, inclusions were glassy and essentially manganese silicate in composition, again with areas of a polycrystalline, titanium-rich phase on the surface. The interinclusion spacing varied little with weld metal oxygen content in the range 0·0268–0·0858 wt-%. The spacing was found to be of a similar order to the acicular ferrite grain size. The titanium-rich surface phase in all the welds was of fcc structure with a lattice parameter of 0·42 nm, which suggests a mixture of TiO and TiN, possibly rich in TiO. The spinel phase was also fcc and had a composition between galaxite (Al₂O₃MnO) and γ-alumina. Both these phases have a low lattice misfit with ferrite. A low lattice misfit of the inclusion surface layers with ferrite coupled with closely spaced inclusions would seem to be key factors in the development of an acicular ferrite weld metal microstructure.

MST/543     

Influence of nickel on microstructure and mechanical properties of medium-manganese steels

To combine the advantage of density reduction and excellent performance, nanometer-sized B2 particles were introduced into the δ ferrite matrix of high-aluminium low-density steel by the addition of nickel (Fe–0.2C–11Mn–6Al–4/8Ni). Compared to Fe–0.2C–11Mn–6Al (0Ni) steel, the hardness and tensile strength of 4Ni and 8Ni steels are significantly improved. The improvement of tensile strength in 4Ni and 8Ni steels was primarily contributed by the precipitation strengthening or solution strengthening of B2 particles in δ ferrite. At the higher annealing temperature, the original dislocation density in δ ferrite is lower. However, dislocation multiplication during tensile deformation was more significant in the sample annealed at higher temperature, which was responsible for a higher work hardening rate.     

Mechanochemical synthesis and shock wave consolidation of TiN(Al) nanostructure solid solution

This paper aims to report the study of the synthesis of a titanium nitride nanostructure solid solution through the reduction of aluminum nitride with titanium based on the stoichiometric reaction of 2Ti + AlN by mechanical alloying (MA) process at a ball-to-powder weight ratio of 15:1. A nanostructure solid solution of in-situ titanium nitride was formed through exchange reaction between Ti and AlN at the initial time of MA. XRD, SEM, EPMA, TEM, and particle size analysis (PSA) were used to characterize the products. It was found that the amount of Al resulting from decomposition of aluminum nitride dissolved in the TiN lattice increased in accordance with milling time, leading to the formation of TiN(Al) solid solution and a reduction of the TiN lattice interplanar distance. The milled powder displayed equiaxed morphology and a narrow size distribution of about 1 μm at the end of the milling process. In-situ TiN(Al) crystallites were of an average size of 6 ± 2 nm. Subsequent to MA, an underwater shock compaction method was applied to the prolonged milled powders to obtain bulk sample. The effect of this shock compaction on the selected sample resulted in the preservation of its nanostructure characteristics with no additional phase transformation which are considered advantageous in the use of high dynamic compaction method for ceramic materials.     

变质和热处理对高强度铸造Al-Cu-Si-Mn合金组织和性能的影响

通过变质处理和热处理实验,研究了不同的Ti变质加入量和固溶时效处理对高强度铸造Al-Cu-Si-Mn合金组织和性能的影响.结果表明,试验材料的铸态组织为粗大的α(Al)固溶体和其晶界分布的θ(Al2Cu)及T(Al12CuMn2)相,加入0.15%～0.2%Ti变质处理可以细化试验材料的铸态组织,变质处理后进行固溶和时效处理,组织由α(Al)固溶体和其晶内弥散分布的二次T相组成,晶界处残留有未完全固溶的T(Al12CuMn2)相,组织中出现α(Al)晶界无析出区.Ti变质处理高强度Al-Cu-Si-Mn合金组织对壁厚效应的敏感性不明显.     

Precipitation Behavior of TiN in Bearing Steel

The precipitation behavior of titanium nitride (TIN) in bearing steel and effects of TiN inclusions on quality of the steel have been studied by thermodynamic calculation and experiment. The results show that with the increase of the content of Ti and [N], the properties of bearing steel decreased; adjusting the content of N and Ti could influence the precipitation occasion and condition of TiN in the steels. If Ti content is less than 30x10-6 and nitrogen content is less than 53x10-6, the temperature of TiN precipitation is under the solidus temperature and the size "\s small so that they have little harmful and even beneficial effect on the properties owing to grain refinement.     

Oxidation of nano-multilayered AlTiSiN thin films between 600 and 1000 degrees C in air

Multilayered AlTiSiN films with a composition of 32.0Al-12.4Ti-4.9Si-50.7N (at.%) were deposited on a steel substrate in a nitrogen atmosphere by cathodic arc plasma deposition. The films consisted of crystalline approximately 8 nm-thick AISiN nanolayers that originated from the Al-Si target and approximately 3 nm-thick TiN nanolayers that originated from the Ti target. Their oxidation characteristics were studied between 600 and 1000 degrees C for up to 20 h in air. They displayed good oxidation resistance due to the formation of a thin, dense Al2O3 surface scale below which an (Al2O3, TiO2, SiO2)-intermixed inner scale existed. They oxidized slower than TiN films because protective Al2O3-rich scales formed on the surface. However, they oxidized faster than CrN films because impure Al2O3 scale formed on the AlTiSiN film. Their oxidation progressed primarily by the outward diffusion of nitrogen and substrate elements, combined with the inward transport of oxygen that gradually reacted with Al, Ti, and Si in the film.