Mn含量对铸造高铌TiAl合金组织和性能的影响

选择两种Mn含量不同的高铌TiAl合金Ti46Al8Nb2Mn0.2B和Ti46Al8Nb1.3Mn0.2B,通过热等静压(HIP)及后续热处理,结合组织和力学性能的分析,研究了Mn含量对高铌TiAl合金的组织和性能的影响.XRD和SEM背散射电子实验结果表明:Mn含量较高的Ti46Al8Nb2Mn0.2B合金,经热等静压及循环热处理,得到的双态组织较粗大,并且有少量脆性β相存在;Mn含量较低的Ti46Al8Nb1.3Mn0.2B合金,经热等静压后直接在双相区长时间保温处理,得到了细小的双态组织,并且完全消除了β相.室温拉伸实验表明,Mn含量的降低提高了Ti46Al8Nb1.3Mn0.2B合金的力学性能,其延伸率、屈服强度和断裂强度分别达到2.4%、548MPa和660MPa.断口形貌分析表明,室温下两种合金都属于解理断裂.     

Tensile properties of mechanically alloyed/milled Ods-Ni-Based alloys

Oxide dispersion strengthened (ODS) NiCr20 alloys were produced by ball milling blends of either prealloyed NiCr20 and yttria powders or elemental Ni and Cr powders and yttria powder. After milling, the powders were degassed in a vacuum furnace, sealed in steel cans, and consolidated by hot extrusion. The mechanical alloying process, which occurs during ball milling of elemental Ni and Cr powders, as well as the changes of microstructure, which occur during milling and extrusion, were characterized by X-ray diffraction (XRD) techniques. Measurements of microhardness, tensile strength, and elongation of extruded bars were done to gain information about the dispersoid parti-tioning and about the relation between milling parameters, microstructure, and tensile properties. These investigations showed that the attainable quality of ODS NiCr20 alloys is higher if they are produced by milling elemental Ni and Cr powders and yttria powders. Besides the dispersoid par-titioning, the homogeneity of the mechanically alloyed powder strongly affects the quality. High-quality materials are only produced if the ball milling process yields a homogeneous dispersoid partitioning and a completely mechanically alloyed NiCr20 solid solution.     

Effect of microstructure on mechanical properties of as-cast Mg-Al alloys

The mechanical properties of Mg-Al alloys are mainly determined by the microstructure, i.e., the amount and morphology of the phases, but also by the presence of defects arising from the melt handling and casting process. In order to obtain information about the isolated effect of the microstructure, it is, therefore, necessary to minimize the amounts of defects. In this study, this has been achieved by remelting and solidifying the alloys in a gradient furnace. The drawing rate was varied from 0.3 to 6 mm/s, which yielded a wide variety of microstructures. Three samples were produced for each parameter set, in order to have a statistical basis for the evaluation. The results showed that homogeneous and reproducible samples could be produced, and that the tensile properties obtained showed a very small scatter. The effects of microstructural parameters such as grain size, secondary dendrite arm spacing (SDAS), eutectic fraction, and eutectic morphology on the yield strength, ultimate tensile strength (UTS), fracture elongation, and hardness has been investigated.     

添加球磨粉末对铁基高温合金锻态显微组织与力学性能的影响

采用SEM、能谱分析、XRD、密度和室温拉伸性能测定相结合的方法,研究添加球磨粉末对铁基高温合金锻态组织和力学性能的影响.结果表明:添加球磨粉末的混合粉末锻造合金的显微组织由几百纳米的细晶粒和几十微米的粗晶粒组成,具有明显晶粒尺寸双峰分布特征,其中细晶粒的形成提高了合金的界面能,有利于元素的扩散、成分均匀化和孔隙的消除...     

Effect of cobalt addition on microstructure and mechanical properties of tungsten heavy alloys

The present investigation attempts to study the microstructure and mechanical behaviour of tungsten heavy alloys with different cobalt content. Alloys with 2 and 3% cobalt were synthesized using liquid phase sintering technique. The alloys were then vacuum heat treated and finally swaged. Quantitative microstructural analyses were undertaken by determining tungsten grain size, contiguity of tungsten and volume fraction of the matrix etc. Tensile results showed that the alloy with 3% cobalt exhibited inferior properties as compared to 2% cobalt alloy. Detailed microstructural and fractographic analysis were undertaken in order to understand these trends. Work hardening analysis showed the double slope behaviour of the alloys, which could be attributed to change in deformation behaviour from single phase matrix to two phase aggregate. It was also concluded that higher cobalt alloys needed further optimization in terms of thermo-mechanical treatment in order to realize their full potential in terms of mechanical properties.     

回归再时效对超高强铝合金力学性能及组织的影响

在传统的回归再时效(retrogression and re-aging,RRA)工艺(峰时效)基础上降低预时效或再时效温度,对Fe和Si杂质含量高的超高强Al-Zn-Mg-Cu合金挤压棒材进行RRA处理,通过拉伸性能和疲劳性能测试以及扫描电镜和透射电镜观察,研究RRA工艺对合金力学性能与组织的影响。结果表明:降低预时效或再时效温度都可明显提高该合金的塑性和抗疲劳损伤性能,略微降低合金的抗拉强度。采用峰时效温度(120℃)RRA处理后的合金,晶内的主要析出相为尺寸较大的η′相,不能被位错切割,合金强度较高(674 MPa),但塑性和抗疲劳损伤性能差,伸长率为11.1%,最终应力强度因子幅值ΔK=26.8 MPa·m1/2;降低时效温度可增加析出相中GP区粒子的比例,减小η′相的尺寸,从而提高塑性变形能力以及抗疲劳损伤性能。     

Effect of lithium on the mechanical properties and microstructure of sic whisker reinforced aluminum alloys

Aluminum-silicon carbide whisker composites containing nominally 3 to 5 pct Li in the matrix alloys have been fabricated and tested. Tensile and compression tests have been conducted at room temperature, and compression creep tests have been conducted at elevated temperatures. Lithium additions were found to increase the strengthening effect of silicon carbide whiskers at room and elevated temperatures. Lithium also reduced the density of the composites and increased the elastic modulus. Transmission electron microscopy showed no obvious chemical reaction between the whiskers and the aluminum-lithium alloy matrix.     

Zn含量对AlMgSiCu合金组织和力学性能的影响

使用常规铸锭冶金方法制备了不同Zn含量的AlMgSiCu合金.利用光学显微镜、扫描电镜、拉伸测试和纳米压痕方法研究了Zn含量对铝合金微观组织和力学性能的影响.研究发现Zn元素能够轻微细化AlMgSiCu合金铸态组织.随着合金中Zn含量的增加,铸态铝合金的晶界变宽,晶界析出相增多.Zn的添加未影响铸态合金的相组成和形貌.随Zn含量的增加,铝合金的强度和延伸率呈现先增后降的变化趋势,添加质量分数0.5%Zn可使合金具有最高的强度,而0.75%Zn使合金获得最高延伸率.对含Zn铝合金的纳米压痕测量表明:随着Zn含量的增加,铝合金的弹性模量呈现逐步降低的趋势.     

Study on microstructure and mechanical properties of as-cast Mg-Sn-Nd alloys

Microstructure, tensile properties and compressive creep behaviors of Mg-(1.65-11.52) wt.% Sn-2 wt.% Nd alloys were studied in this paper. The microstructure of the as-cast Mg-Sn-Nd alloys consisted of dendritic α-Mg, Mg2Sn and Mg-Sn-Nd ternary phase containing rare earth element. The highest ultimate tensile strength of 140 MPa and percentage elongation after fracture of 9.7%, were achieved with a composition of Mg-8.23 wt.% Sn-2 wt.% Nd. The compressive creep resistance of Mg-8.23 wt.%Sn-2 wt.% Nd alloy w...     

Ca和Sr对铸态Mg-Sn-Si合金组织和性能的影响

用X射线衍射仪(XRD)、扫描电镜(SEM)、光学显微镜(OM)研究了铸态Mg-Sn-Si-Ca-Sr合金的相组成和显微组织,用力学性能试验机测定了合金的拉伸性能.结果表明,Mg-5Sn-xSi-0.5Ca-0.5Sr(x=1,2)合金由α-Mg、Mg2Sn、Mg2Si和CaMgSn相所组成,Mg2Si相含量随Si元素的增加而增加.对于Mg-5Sn-1Si-yCa-0.5Sr(y=0.5,2)合金,Ca的质量分数提高到2%后会促进Mg2Ca相和CaMgSn相形成,但同时抑制了Mg2Sn、Mg2Si相的析出,从而导致合金性能下降.对于Mg-5Sn-2Si-0.5Ca-ySr(y=0.5,2)合金,当Sr的质量分数由0.5%提高到2%时,Mg2Si和Mg2Sn相均得到显著细化,并促进了基体内MgSn(Sr,Ca)相形成,从而提高了合金的抗拉强度与屈服强度.     

Nb含量对机械合金化Cu-Nb合金组织与性能的影响

在金属铜粉中分别加入1.5%和6%的Nb粉(质量分数),通过机械合金化和800℃/2 h/30 MPa条件下真空热压,制备Cu-1.5%Nb和Cu-6%Nb合金,采用X射线衍射仪(XRD)、扫描电镜(SEM)、透射电镜(TEM)以及电导率与硬度测试,研究Nb含量对合金微观组织结构与性能的影响。结果表明,通过机械合金化得到的Cu-1.5%Nb和Cu-6%Nb复合粉末,Cu相平均晶粒尺寸分别约为17和13 nm。Nb含量增加有助于抑制Cu晶粒长大,热压Cu-6%Nb合金中Cu相的平均晶粒尺寸保持纳米级(65 nm),而Cu-1.5%Nb合金的Cu晶粒平均尺寸为亚微米级,约为110 nm。热压过程中脱溶析出的Nb颗粒尺寸分布为双模态,既有尺寸大于100 nm的粗大Nb粒子,也有尺寸小于10 nm的纳米Nb粒子。与Cu-1.5%Nb合金相比,Cu-6%Nb合金的显微硬度(HV)提高了112,但电导率降低约7.54×10~6 S/m。细晶强化和弥散强化是Cu-Nb合金的主要强化机制。     

Effect of Sn on microstructure and mechanical properties of Ti-base dendrite/ultrafine-structured multicomponent alloys

Ti_57−x Cu₁₅Ni₁₄Sn_4+x Nb₁₀ (x = 0, 5, or 10) alloys were prepared by copper mold casting. At Sn = 4 at. pct, a dendrite/ultrafine-structured multicomponent alloy was obtained, which exhibits 1271 MPa yield strength, 77 GPa Young’s modulus, and 2 pct plasticity at room temperature for 3-mm-diameter samples. The cooling rate significantly affects the as-cast microstructure and the mechanical properties. For 5-mm-diameter samples, the alloy exhibits 1226 MPa yield strength, 63 GPa Young’s modulus, and 2.5 pct plasticity. At Sn = 9 at. pct, Ti-, Sn-, and Nb-rich particles precipitate primarily. This near-hypereutectic alloy composition leads to the precipitation of intermetallics, which deteriorate the mechanical properties and result in the coexistence of ductile and brittle fracture mechanisms. At Sn = 14 at. pct, the alloy composition is completely in the intermetallic region, thus inducing the formation of Ti₂Cu, Ti₂Ni, and Ti₃Sn intermetallics. The alloy becomes very brittle because the intermetallic compounds dominate the fracture process.     

硼元素对FB2钢组织和力学性能的影响

 为了研究硼含量对FB2钢组织和力学性能的影响,先对5组不同硼含量的FB2钢用维乐试剂(1 g苦味酸+5 mL盐酸+100 mL无水乙醇)浸泡腐蚀90 s后进行形貌观察与分析。通过SEM-EDS观察分析基体中M₂₃C₆型碳化物,然后用Image-pro plus软件对析出相的尺寸进行分析。接着采用日本岛津制造所生产的AG-XPLUS 100 kN万能试验机,对5组不同硼含量的FB2钢进行室温拉伸试验和室温冲击试验。最后对5组不同硼含量的FB2钢进行组织和力学性能的分析。结果表明,FB2钢中的硼元素可以抑制M₂₃C₆型碳化物的长大粗化,但是硼元素易于与氮元素形成BN夹杂物。随着硼含量的增加,M₂₃C₆型碳化物的平均尺寸呈现降低的趋势,BN夹杂物的单位数量和平均尺寸呈现增大的趋势。FB2钢的室温拉伸性能随着硼含量的增加先升高后降低,并且在硼质量分数为0.010%时FB2钢的室温拉伸性能达到最强。当硼质量分数由0增加到0.010%时,FB2钢的室温拉伸性能升高,这是由于硼元素的加入抑制了M₂₃C₆型碳化物的粗化,从而提升了FB2的强度;当硼质量分数由0.010%增加到0.030%时,FB2钢的室温拉伸性能降低是由于硼元素与氮元素结合形成了BN夹杂物,引起应力集中,且大尺寸的BN夹杂物诱发了孔洞的形成,降低了FB2钢的性能。FB2钢的冲击功随着硼含量的增加呈现降低的趋势,且当硼质量分数为0.020%和0.030%时,冲击功出现了骤降,这是由BN夹杂物的单位数量、平均尺的上升和大尺寸BN及杂物的析出导致的。     

Effect of initial microstructure on microstructural instability and creep resistance of XD TiAl alloys

A number of lamellar structures were produced in XD TiAl alloys (Ti-45 at. pct and 47 at. pct Al-2 at. pct Nb-2 at. pct Mn+0.8 vol pct TiB₂) by selected heat treatments. During creep deformation, microstructural degradation of the lamellar structure was characterized by coarsening and spheroidization, resulting in the formation of fine globular structures at the grain boundaries. Grain boundary sliding (GBS) was thought to occur in local grains with a fine grain size, further accelerating the microstructural degradation and increasing the creep rate. The initial microstructural features had a great effect on microstructural instability and creep resistance. Large amounts of equiaxed γ grains hastened dynamic recrystallization, and the presence of fine lamellae increased the susceptibility to deformation-induced spheroidization. However, the coarsening and spheroidization were suppressed by stabilization treatments, resulting in better creep resistance than the microstructures without these treatments. Furthermore, well-interlocked grain boundaries with lamellar incursions were effective in restraining the onset of GBS and microstructural degradation. In the microstructures with smooth grain boundaries, a fine lamellar spacing significantly lowered the minimum creep rate but rapidly increased the tertiary creep rate for the 45 XD alloy. For the 47 XD alloy, well-interlocked grain boundaries dramatically improved the creep resistance of nearly and fully lamellar (FL) structures, in spite of the presence of coarse lamellar spacing or equiaxed γ grains. However, it may not be feasible to produce a microstructure with both a fine lamellar spacing and well-interlocked grain boundaries. If that is the case, it is suggested that the latter feature is more beneficial for creep resistance in XD TiAl alloys with relatively fine grains.     

Mg含量对Al-4.8Cu-xMg-1.0Ag合金组织与力学性能的影响

通过对显微硬度与疲劳裂纹扩展速率的测试以及扫描电镜和透射电镜观察等实验手段,研究Mg含量对Al-Cu-Mg-Ag合金时效析出过程与力学性能的影响.结果表明:随着Mg含量的上升,合金的时效响应速率加快,而硬度则先上升后下降,在Cu/Mg质量比接近6时,合金硬度最高;Mg含量的提高可为主要析出相Ω相提供更多的形核位置,使得...     

超细SiC颗粒对球磨制备纳米晶AZ91镁合金组织及性能的影响

通过机械球磨制备了SiC颗粒（SiC_p）增强镁基复合材料粉末（AZ91?xSiC_p,x=5%、10%、15%,体积分数）,实现了镁基体纳米化及亚微米级SiC_p在镁基体中的均匀弥散分布,研究了SiC_p对球磨后粉末微观组织的影响规律。结果表明,SiC_p第二相的引入能够促进机械球磨过程中镁基体晶粒的细化,晶粒细化程度随SiC_p体积分数的增加有所加强,同时SiC_p含量的提高对Al元素在镁基体中的固溶及其自身颗粒的细化起到抑制作用。球磨后AZ91?xSiC_p（x=5%、10%、15%）复合粉末的硬度分别为HV 166、HV 175和HV 185,强化机制为细晶强化、弥散强化、固溶强化和承载强化,计算得到AZ91?5%SiC_p复合粉末不同强化机制所引起的强化效果占比分别为86.9%、7.4%、1.8%和3.8%。     

时效热处理对7B50超强铝合金组织与性能的影响

通过拉伸试验、维氏硬度测试、电导率测试、晶间腐蚀与剥落腐蚀试验、金相观察及透射电镜分析等,研究新型的4级时效工艺(four-step aging,FSA),即高温短时效—低温长时效—高温短时效—低温时效工艺对Al-Zn-Mg-Cu系7B50超强铝合金组织和性能的影响。结果表明:FSA处理促使7B50铝合金晶界析出相发生球化和细化,晶界析出相的体积分数显著增大并呈非连续分布;与传统的回归再时效RRA工艺相比,经过优化的新型4级时效热处理能明显提高7B50铝合金的力学性能和抗腐蚀性能;经过150℃/5 h→110℃/24 h→150℃/5 h→110℃/12 h的4级时效处理后,合金的室温抗拉强度从582 MPa提高到685 MPa,抗腐蚀性能明显超过回归再时效(RRA)处理的合金。     

微合金元素B对轻质TWIP钢组织及力学性能的影响

摘要：将质量分数为0.002%的微合金元素B加入至Fe-28Mn-9Al轻质TWIP钢中,以期改善其强塑积及室温冲击性能。利用X射线衍射、扫描电镜、电子万能拉伸试验机和金属摆锤冲击试验机对热轧TWIP钢的物相组成、微观组织、力学拉伸性能及室温冲击韧性进行了研究与分析。结果表明,微合金元素B的添加具有延缓奥氏体向铁素体转变的作用,细化了奥氏体晶粒,提升了钢的力学性能,TWIP钢的塑性、强塑积和冲击韧性均有明显的提高。     

Sintering time and atmosphere influences on the microstructure and mechanical properties of tungsten heavy alloys

The mechanical properties of tungsten heavy alloys are sensitive to the processing cycle and are adversely affected by residual porosity. Sintering times greater than 2 hours usually result in pore growth with degraded properties. The development of an optimized sintering atmosphere has allowed exploration of long sintering times without significant property degradation due to pore growth. The optimal cycle was used to sinter two heavy alloy compositions (88 and 95 wt pct W) for times up to 600 minutes at 1480 °C. The 88 pct W samples slumped, but the 95 pct W samples were fully densified and suitable for tensile testing. At long sintering times, the tungsten grains flattened and the tungsten contiguity decreased, indicating a transition to low-energy configurations for the solid-liquid interfaces. The cube of the mean grain size varied linearly with the isothermal sintering time. This allowed determination of grain size effects on mechanical properties, showing a decreasing yield strength with increasing time in agreement with the Hall-Petch behavior. The tensile strength and elongation were highest for sintering times from 30 to 90 minutes, reflecting a minimum in the residual porosity.