浇铸钛和金的显微结构和机械性能外文翻译、中英文翻译、外文文献翻译

1 附录一         浇铸钛和金的显微结构和机械性能  摘要： 通过感应熔化的方法而获得的 Ti21523合金，研究热处理和冷却凝固率对其显微结构和机械性能的影响和作用。结果表明：通过增加冷却凝固率，可以使 Ti21523合金的显微结构从单一化特征及大尺寸的粒状结构变成了具有优良性能的小尺寸粒状结构。通过采用不同的方法和对不同时期的合金进行处理，合金相位逐渐在粒状晶体的内部和粒状晶体的边界上沉淀。由于沉淀物晶相的改变，合金承受拉力的性能和伸长率同时被改良。在 b=1. 406Gpa、 =4. 5%时，将会获得一种具 有良好性能的合金 ,在临界区域里使用这种合金会让我们收到满意的效果。  关键字  浇铸 Ti21523合金；冷却凝固率；机械性能  1 介绍  钛合金以其优良的机械性能，在飞机、航空航天和其它领域中，受到了人们的关注和认可，尤其是在较高特殊作用力的环境之下。在降低航天器的质量并改进的它的运输适宜性上，该合金受到了关注。为了满足以上两种情况，一种被叫做贝它钛的重要钛合金逐渐得到发展和优化。由于其具有高抗力、弹性系数和伸长率等良好的综合性能，合金  Ti215V23Cr23Sn23Al(Ti21523) 已经变成了潜在的选择 材料被用于在那些贝它类型合金之中。从以上的论述中我们可以知道， Ti21523合金在室温有较好的可使用性，同时也适用于寒冷的工作环境之下。不幸地是，由于合金的高处理成本以及诸如低可塑性和高刚度等缺点，使其在制造复杂的联合体和薄壁件时存在许多问题，成为影响其在航空航天业中广泛应用的关键所在。为了降低其合成成本并达到其易于重新塑造的弹性，精密铸造技术被引入到了这个领域中。但是由于铸造出来的合金其贝它晶粒较大且机械性能很低，故此 Ti21523合金的使用受到了极大的限制。由于热处理对 Ti21523合金的力有影响，因此 Ti21523合金还是可以改善其伸长率并提高它的机械性能的。关于热处理对 Ti21523合金的影响的研究首先在美国和前苏联开展。他们指出：在热处理之后，在阿尔法晶相的内部和边界上均出现了矩阵式的沉淀物，阿尔法相的出现与分布戏剧性地改善了合金的机械性能。这篇文章的目地就是要找出在 2 不同的冷却凝固率和热处理条件下钛合金的机械性能和微观结构的变化，以找到一个科学合理的方法来测量和进一步提高合金的机械性能。  2 实验  实验的原料来自海棉状的钛 ,矾和铝的合金，高纯净的铝块，铬粉和锡块。  然后他们在一起在感应炉里被融化，依 照合金名义上的组成成份，其组成成份有 15% V、 3% Al、 3% Cr、 3% Sn，其余的全部是 Ti。装料的总重量是 18千克。我们设置旋转式喷灌器工作转速为 200转 /分，分布的温度大约是 1750。为了研究合金不同的 冷却凝固率对于其机械性能和微观结构的影响，熔化的合金离心后被浇注到一个长 235mm，宽 100mm，厚度分别为 50mm、 25mm、 10mm的一系列金属模具内。用于分析合金的微观结构和机械性能的样品就来自于其中。热处理的试样在 800下被加热 20分钟，然后水冷。其他用空气冷却的试样也是如此。合金的显 微结构被放在高倍显微镜下和TEM机上进行研究。拉伸试验后的物理断面也被放在 SEM机下进行研究。它的机械特性是在 Instron 1186电子拉伸机上进行测试的。  3 结果及讨论  3.1冷却凝固率对合金微观结构的影响  合金在冷却凝固后的微观结构如图 1所示 .带有少许气体和热力孔的等轴 晶粒在合金晶粒的内部和边界上均有分布。带有黑色的第二幅图被认为是一个不平衡的冷却凝固结构。随着冷却凝固率的不断增加，晶粒的尺寸变得越来越小。越靠近模型的内表面晶粒的尺寸越小，越小的铸造尺寸结果也是如此。这是因为在模型的内表面以及较 小的铸造尺寸时，激冷作用对合金的晶粒尺寸并没有多少不同之处  3.2冷却凝固率对合金机械性能的影响   3 下表 1列出了不同的冷却凝固率对合金延展性的影响。随着冷却凝固率的增加，合金承受的拉力也随之增加，与此同时，合金的延伸率也逐渐升高。延展率的增加主要归因于较小的晶粒尺寸。比较较薄的部分而言，中等厚度及较厚区域在延展性方面并没有太大的不同之处。   3.3热处理后的合金微观结构   4 在正常情况下，通过空冷和小冷的合金单 是可以区分开的。经过不同时期和不同方法的处理之后，针状的 相出现在了晶粒的内部以及边界上，良好的拉伸 和延伸率的结合是可以通过恰当地热处理来达到的。图 2的（ a）和（ b）中展示了 TEM假想的在 450到 650 5 时加热 8小时后的合金显微结构。随着温度的逐渐升高，针状的 相变得粗糙。 相与其基体之间存在着互不相干的相互关系。图 2（ c）中显示出 相析出于晶粒的边界上， 相与晶粒边界所成的角度估计 30。 相之所以很容易在晶粒的边界上析出的原因可以归结为较 6 低的成核能量以及不完全处理后在晶粒的边界上所产生的元素相互排斥作用。在晶粒的边界上大量的析出 相将导致合金的脆性。图 3（ a）和（ b）中展示出了 TEM机假想的在 450下加热 6小 时和 24小时时的合金相图。随着加热时间的增加， 相变得越来越粗糙。同时， 7 相也会部分的增加。图 3（）中展示出了 TEM机假想的双期处理后的合金的对比。双期处理后的 相变得更加粗糙，在 相的析出物上有很长一段的距离。      3.4热处理后合金的机械性能                                   图 4（ a）中表示了在不同的加热温度下加热 8小时后合金机械性能的变化。随着加热温度的逐渐增加，伸长率和屈服强度下降而伸展率增加。导致合金机械性能变化的主要原因是晶粒的大小，数量以及 基体上的 相。随着加热温度的不断增加， 相变得越来越粗糙，从而导致了该相越来越容易析出并附着在原有的晶粒上。在进行机械性能测试的过程中， 相最终导致了合金的低强度和高的延展性。当加热温度为 450时，b等于1.406GPa,当加热温度为 650时，b等于 905MPa。对比于强度而言，合金延展率的变化有不同的倾向，延展率从 4.5%（ 450）变为 14.4%（ 650）。  图 4（ b）中展示出了在 450下加热不同时间后合金机械性能的变化。随着加热时间的不断增加，合金的伸长率和屈服强度稍有增加而延伸率却下降了。随着加热时间的继续增加，析出物的距离变得特别小，从而很难再析出，以致于导致了在测试的过程中，金属的强度升高而延伸率下降。  图 5显示出了在 450和 650下加热 8小时后的合金破碎形态。结果显示出破碎是在内部出现的表现出涟漪的特性。虽然破碎是内部的微粒，但是相对较小的微粒尺寸也许是高延展性的 8 最好解释，合金二期加热后，强度增加而延展性下降，b下降到了386兆帕。延展率提高到 3.5个百分点，二期处理之后，析出物之间较长的距离是导致合金低强度和高延展性的主要原因。  3.5热处理后冷却凝固率对合金机械性能的影响  图 6显示出了热处理之后合金中等厚度和较厚部分的机械性能，试样在 800摄氏度下完全处理20分钟之后在不同的温度下加热 8小时。随着加热温度的逐渐增加，中等厚度和较厚区域合金的拉伸力下降而延展率升高，总的来说，合金中部的伸长率和延展率都比较厚部分的高，但是当温度厚度部分高于 510摄氏度时加热 8小时后，合金中等厚度部分的伸长率和延展率却都比较厚部分的低。  这个不期望的后果可以由晶粒从边界向晶粒内部逐渐混合，从而导致了内部应力起作用而获得解释   s= i+ kL d- 1/2          (1) 其中 i是断层混乱运动中磨擦力的反作用力。  kL是一个常量， d是晶粒直径。  晶粒内部应力 可以由 Ashby的 Orowan公式来描述。  =Gb/2 ( D- l) ln l/ r0       (2) 其中 G是剪切模量， b是伯格斯向量， r0=4b,D是析出物之间的距离， L是析出物的厚度。当考虑到拉伸屈服作用力的时候，我们便可以推断出多晶材料时：   =1/2 晶粒边界应力和内部应力的混合作用关系式可以表示为：   s= i+ kL b- 1/2+ Gb/ ( D- l) ln l/ r0(3) 增加晶粒的尺寸将会导致屈服强度的下降，但同样可以导致在晶粒内部的析出物的密度变大，从而使析出物之间的距离减小，比 9 较较小尺 寸的晶粒而言，较大尺寸的晶粒在晶粒内部的析出物在对伸长率的影响与作用上占有优势。当在 510摄氏度下加热 8小时后，大尺寸晶粒的伸长率在晶体内部的析出物中要远远超过小尺寸的晶粒。  4 结论  （ 1）凝固后的合金的微观结构是由各方等大的 晶粒和在晶体边界和内部的一些气泡和热力孔所组成。随着冷却凝固的增加，合金的晶粒尺寸变小，伸长率和屈服强度增加。同时，合金的延展率升高。  （ 2）随着加热温度的升高和加热时间的增加，针状的相变得粗糙。同时，相的碎片数量也随之增加，二期处理后相变得更加粗糙。  （ 3）随着加热温度的升高，伸 长率和屈服强度下降而延展率升高，随着加热时间的升高，伸长率和屈服强度稍有升高而延展率下降而伸长率下降。  （ 4）总体来说，中等厚度部分的合金的伸长率和延展率均比较厚部分的高，各项性能的最好结合是在b等于 1.406GPa,为 4.5%时获得的。它可以满足临界领域这种合金的使用要求。    10 附录 2 Microstructure and mechanical properties of high strength as cast Ti21523 alloy Abstract： The effects of heat treatment and solidification cooling rate on the microstructure and mechanical properties of as cast Ti21523 alloy prepared by induction skull melting method were investigated. Results show that the microstructure of as2cast Ti21523 alloy changes from the features of simplified and larger size of beta grains to finer grain size with increasing solidification cooling rate. After solution treatment and different ageing treatment, alpha phase precipitates in grains interior as well as in grain boundaries. Due to the modification of the precipitate phase, the tensile strength and elongation of the alloy are improved simultaneously. A good combination of the values of of and 4. 5 % of was obtained , which will be satisfied the use of this kind of alloy in critical areas. Key words： cast Ti21523 alloy； solidification cooling rate；  mechanical properties 1  INTRODUCTION Titanium alloys have received appreciated attentions in the fields of aircraft, aerospace, and others owing to their excellent mechanical properties, especially the high specific strength. With regards to lower the mass of aircraft and improving their suitability for transportation , an important class named beta titanium alloys are developed to mee t the requirement of the above situations1 ,2 . As the result s of good  properties combination of high eremitic strength, elastic modulus and elongation, the alloy Ti215V23Cr23S n23Al (Ti21523) has become a potentially selective material to be used among those beta type alloys 3 .From Ref. 4, it is known that the alloy Ti21523 has good workability at room temperature and suitable for cold working. Unfortunately, the high processing cost and drawbacks of low plasticity  11 and high deformation force of the alloy have made it difficult to produce complex and thin walled components that are being the keynotes for aero applications 5. In order to reduce the processing cost and reach the flexibility of shaping Ti21523 alloy, the technique of precision casting has been involved in the field. But due to the large beta grain size and lower mechanical properties under casting condition, the usage of the as2cast Ti21523 alloy is limited. Because of the strengthen effects of heat treatment on the beta type titanium alloys, the Ti21523 alloy can somewhat be strengthened to the extent of high level of the mechanical properties. The investigations on the effect s of heat treatment on titanium alloys have been carried out by America and the former Soviet Union 6, 7. As it is pointed out that after heat treatment, the matrix precipitates alpha phase in grain interior and at grain boundaries as well. The appearance and distribution of alpha phase improve the mechanical properties of the alloy dramatically 8. The purpose of this article is to investigate the effect of different solidification cooling rates and heat treatment on the microstructure  and mechanical properties of the alloy in order to find  an efficient measurement to further improve the mechanical properties o f the alloy. 2  EXPERIMEN TAL The experimental raw materials came from spongy titanium, vanadium aluminium master alloy, high purity aluminum block , chrome powder and tin block. Then they were melted in an induction skull melting furnace according to the nominal composition of the alloy which composed of 15 %V, 3 %Al, 3 %Cr, 3 %Sn, and the balance Ti. The total mass of the charge was 18 kg. The pouring parameters were set as the speed of 200 r/ min for rotating table and  the pouring temperature of about 1750 . In order to study the effect of different solidification cooling rates on the solidification microstructure and mechanical properties of the alloy , the molten alloy were centrifugally pouring into a step metal mould with the gauge of 235 mm in length , 100 mm in width , and 50 mm , 25 mm , and 10 mm in thickness respectively. The samples for the analyses of microstructure  and  12 mechanical properties of the alloy came from the step specimen. The samples for heat treatment was solute treated at 800 for 20 min and then water cooling as well as the treatment of different ageing temperatures and  times with air cooling. The microstructure of the alloy was studied with optical microscope and TEM. The morphology of fractures after tensile test was also investigated by SEM. The mechanical properties were tested in model Instron 1186 electric tensile machine. 3  RES ULTS AND DISC USS ION 3. 1  Effect of solidification cooling rate on microstructure of alloy The microstructure of the alloy after solidification is shown in Fig. 1. The equiaxed beta grain is found with a few of gas and shrinking holes in grain interior and at grain boundaries as well. The secondary phases with black color were confirmed as a non equilibrium solidification structure. With increasing solidification cooling rate , the grain size becomes smaller. The grain size is small where attached to the  inner surface of mould or positions with smaller casting size because of the action of chilling effect of mould inner surface and smaller casting size on the alloy. Compared with the thin section, the middle and thick section have less difference in grain size.  13 3. 2  Effect of solidification cooling rate on mechanical properties of alloy Table 1 has shown the effect s of different solidification cooling rates on the tensile properties of the alloy. With increasing solidification cooling rate , the tensile strength of the alloy increases. At the same time the elongation of the alloy is improved. The increase of strength and elongation attributes to small grain size 9. Compared with the thin section, the middle and thick section has less difference in tensile properties. 3. 3  Microstructure of alloy af ter heat treatment At the normal condition the single beta microstructure for the alloy can be obtained by air cooling and water cooling. After solution treatment and different ageing treatments, acicular alpha phase  is observed at grains interior as well as in grain boundaries. A good combination of strength and elongation can be achieved with proper heat treatment .F igs. 2 (a) and (b) show TEM image of the alloy aged at 450  and 650  for 8 h. With increasing ageing temperature, the acicular alpha phases become coarse. There exist s incoherent corresponding relationship between the alpha phase  and matrix 10. Fig. 2 (c) shows alpha phases precipitate at grain boundaries. The  14 angles between the grain boundaries and alpha phases were estimated about 30 . The reasons for the easy precipitation of alpha phases at grain boundaries can be interpreted as low nucleation energy and the segregation of alloying element at grain boundaries due to the inadequate solution treatment. The large quantity of precipitates at grain boundaries was responsible for the brittleness of the  alloy. F igs. 3 (a) and (b) present TEM image of the alloy aged at 450 for 6 h and 24 h. With increasing ageing time, the alpha phases become coarser. The volume fraction of the alpha phase increases simultaneously. F ig. 3 (c) present the comparison of TEM image of the alloy with duplex ageing treatment. The alpha phases became coarser with a longer distance between alpha precipitates after duplex aged.  15    3. 4 Mechanical properties of alloy after heat treatment Fig. 4 (a) demonstrates the change of mechanical properties of the alloy aged at different temperatures for 8 h. With increasing ageing temperature , the tensile strength and yield strength decrease and elongation increases. The direct reasons for the change of mechanical properties of the alloy is the size, quantity and dist ribution of alpha phases in the matrix. With raising ageing temperature, the alpha phases become coarse that leads to the more easiness for dislocations to cross the precipitation during the test process so that the strengthening action of the alpha  phase lessens which will cause the lower strength and  higher elongation of the alloy. When the ageing temperature is 450 , b equals to 1. 406 GPa. While the ageing temperature is 650 , b equals to 905 MPa. Compared with the strength, the elongation of the alloy has different change trends. The elongation is from 4. 5 % (450 ) to 14. 4 % (650 ) . Fig. 4 (b) demons rates the change of mechanical properties of the alloy aged at 450  for different times. With increasing ageing time, the tensile  strength and yield strength increase a little with the decrease of elongation. With prolonging the ageing time, the distance between the precipitations become nearly that leads to the more difficulty for dislocations to cross the precipitations during the test process, which cause the higher strength and lower elongation.  Fig. 5 shows the fracture morphology of the alloy aged at 450 and 650 for 8 h. It has shown that the fracture is inter granular characterized by dimples. Although the fractures are inter granular , the relatively smaller grain sizes maybe the better explanation of  16 the high elongation. When the alloy is duplex aged, the strength decreases with increase of elongation. b has been cut down by 386 MPa. The elongation has been improved by 3. 5 %. The longer distance between the precipitations after duplex aging is responsible for the lower strength and higher elongation. 3. 5 Effect of solidification cooling rate on mechanical properties of alloy after heat treatment Fig. 6 presents s the mechanical properties of the alloy which locate in the middle and thick section after heat treatment. The samples were solute treated at 800 for 20 min and then ageing at different temperatures for 8 h. The tensile strength of the alloy from both the middle and thick section decreases with the increase of elongation when the ageing temperature increases. As a whole, the tensile strength and elongation of the alloy from middle section are higher than that from the thick section. But aged at or above 510 for 8 h , the tensile strength of the alloy from middle section is lower than that of the thick section. This unexpected behavior can be explained by means of model which incorporate the contribution of the grain boundaries to and the grain interior to the tensile strength 8.The contribution of the grain boundaries to s can be expressed by the well known Hall Petch relationship   s = i + kL d - 1/ 2 (1) Where i is the friction stress opposing to dislocation motion , kL is a constant , and d is the grain  17 diameter.    The contribution of the grain interior to precipitates ( ) maybe expressed by the Orowan equation modified by Ashby11 . = Gb/ 2 ( D - l) ln l/ r0 (2) Where G is the shear modulus , b is the burgers vector and r0 = 4 b , D is the distance between precipitates , l is the thickness of the precipitates. When considering the tensile yield strength it is possible to assume that for a polycrystalline material = 1/ 2 .The combined contribution of grain boundaries and the precipitates in the grain interior is   s = i + kL b - 1/ 2 + Gb/ ( D - l) ln l/ r0 (3) Increasing the grain size would decrease the yield  strength, but would also cause larger precipitate density in the grain interior , which result in a smaller distance between precipitates. Compared with the small grain size , the contribution of precipitates in the  grain interior to the tensile strength is the dominating factor for the large grain size. When aged at or above 510 for 8 h , the tensile strength of large grain size has exceeded the small one due to the relatively stronger strengthening action of the precipitates in the grain interior. 4  CONCLUSIONS 1) The microstructure of the alloy after solidification is the equiaxed beta grain with a few of gas and shrinking holes in grain interior and grain boundaries as well. With increasing solidification cooling rate, the size of grain becomes smaller, the tensile strength and yield strength of the alloy increase. At the same time , the elongation of the alloy is improved. 2) With increasing ageing temperature and also prolonging of  18 ageing time, the acicular alpha phase becomes coarse. The volume fraction of the alpha phase increases simultaneously. The alpha phase becomes coarse after duplex aged. 3) With increasing ageing temperature, the tensile strength and yield strength decrease and the elongation increases. With increasing ageing time the tensile strength and yield strength increase a little and  the elongation decreases. After the alloy is duplex aged, the strength decreases and the elongation increases. 4) The tensile strength and elongation of the alloy from middle section are higher than that from the thick sec