定向凝固Ni3Al合金高温变形后的显微组织特征

利用金相,扫描电镜和透射电子显微镜研究了定向凝固Ｎｉ３Ａｌ合金高温变形后的显微组织特征。研究结果表明,当变形速率较快时,原始柱状晶晶界无明显变化,晶内无明显结构存在;当变形速率较慢,合金呈现塑变形时,变形初期柱状晶晶界呈现“锯齿状”,后期原始柱状晶界消失,代之以晶粒尺度约为１５ｍｍ的晶粒带,晶粒带中既有小角度晶界,也有大角度晶界。     

固溶处理对1种镍基单晶高温合金组织的影响

采用光镜、扫描电镜对1种镍基单晶高温合金的铸态组织和不同温度固溶处理后的组织进行了观察，研究了不同温度固溶处理对γ′相尺寸、γ／γ′共晶、成分偏析的影响。结果表明：合金枝晶间γ′相的固溶温度高于枝晶干γ′相的固溶温度，随固溶处理温度的升高，γ′相尺寸略有增加，γ／γ′共晶量及成分偏析降低；1290℃，4h，AC固溶处理后合金枝晶干、间γ′相全部固溶，1310℃，4h，AC固溶处理后合金中γ/γ′共晶全部消除，1320℃固溶处理时，合金中出现初溶现象；确定1310℃，4h，AC为合金的固溶处理工艺。     

Al含量对高钨铸造高温合金显微组织和高温拉伸性能的影响

对Al含量分别为4.5%、5.5%、6.5%和7% (质量分数,%)4炉高W铸造镍基高温模具合金的显微组织和1100 ℃的高温抗拉强度进行了对比研究,结果表明：4.5%和7%的合金由于主要强化相次生γ′ 含量不足50%(体积分数),且高Al量合金的共晶γ′ 和析出的α(W,Mo)相是1100 ℃下高温强度不高的主要原因。5.5%和6.5%的合金次生γ′ 含量为56%~57%,共晶γ′ 含量为6%~12%,其1100 ℃高温拉伸强度达到同类合金最高水平,为488~518 MPa。目前该合金已用于制造1050~1080 ℃工作的大型等温锻造模具,其Al含量的成分范围为5.5%~6.5%(质量分数)。     

Ag基焊料Ti3Al与Ni基高温合金接头的组织及性能

采用自行设计制备的Ag-Cr-Ni-Cu合金作为焊材,对Ti3Al基合金与GH4169高温合金进行了填丝氩弧焊。采用扫描电镜(SEM)及能谱分析(XEDS)等方法对焊料及接头各区域的微观组织进行了观察和分析,接头中无宏观缺陷产生。Ag-Cr-Ni-Cu合金与Ti_3Al母材结合良好,但与GH4169母材的结合力相对较弱。焊缝由白色Ag-Cu基体中分布Cr,Ag,Ni,Cu,Ti,Al等元素组成的深灰色相组成。GH4169/Ag-Cr-Ni-Cu界面不存在反应层; Ag-Cr-Ni-Cu/Ti_3Al界面处存在宽度约为20μm的反应区域,主要由Ag+AgTi及固溶Cr的(Ti,Nb)固溶体组成。2个界面的硬度均高于母材及焊缝,焊缝硬度最低。接头的平均室温抗拉强度为130 MPa。拉伸试样断裂于GH4169/Ag-Cr-Ni-Cu界面。     

固溶处理对新型镍钴基高温合金显微组织及力学性能的影响

采用OM、SEM和拉伸试验等研究了固溶温度和固溶时间对新型镍钴基高温合金组织及力学性能的影响。结果表明,晶粒尺寸变化与一次γ′相含量变化一致,固溶温度低于1110℃时,随着固溶温度升高或固溶时间延长,残留的一次γ′相钉扎晶界,晶粒尺寸增加较缓。固溶温度为1110℃时,延长固溶时间至4 h时,一次γ′相基本回溶,晶粒尺寸迅速增加,进一步延长固溶时间至6 h时,晶粒尺寸增加减缓,即合金中一次γ′相的全溶温度为1110℃。合金在1100℃固溶4 h和双级时效处理(670℃×24 h,空冷+780℃×16 h,空冷)后的抗拉强度和屈服强度达到最大值,分别为1584 MPa和1104 MPa。因此,合金的固溶温度宜选取为1100℃,固溶时间宜选取为4 h。     

高Cr铸造Ni基高温合金K4648的显微组织

真空感应熔炼高Cr铸造Ni基高温合金K4648,重熔浇注成等轴晶成形试棒.对薄截面试棒和厚截面中柱管浇道进行(1 180℃,4 h)固溶处理和(1 180℃,4 h)+(900℃,16 h)标准热处理.铸态和热处理态试样通过光学金相、定量金相、扫描电镜及能谱分析和X射线衍射分析确定合金中相的种类、形貌和成分.结果表明:K4648合金铸态组织中主要存在γ基体、初生α相和MC碳化物;初生α相是Ni、Mo和w在Cr中的过饱和固溶体,其中Ni含量(摩尔分数)可达30%以上,本研究中的α相可命名为α-(Cr,Ni):在0.2 N载荷下,该α相的维氏显微硬度值为6.3 GPa,是一种硬而脆的相;经(1 180℃,4 h)同溶处理,初生α相和MC碳化物都会回溶,并且转变为M23C6碳化物,M23C6碳化物比初生α相具有更高的Cr含量和更低的Ni含量.固溶处理后特别是在厚截面试样中还残存未转变的α相和MC碳化物.(1 180℃,4 h)+(900℃,16 h)标准热处理后,合金内部广泛析出片状次生α相和γ'-Ni3(Al,Ti,Nb)相,且在晶界区补充析出粒状M23C6碳化物,起到强化合金的作用.     

一种新型Ni3Al基高温耐磨合金的显微组织和性能研究

针对我国新一代航空发动机叶冠表面强化用高温耐磨材料的迫切需求,采用熔炼铸造法制备出一种以碳化铬和NiAl相作为耐磨硬质相的新型Ni₃Al基高温耐磨合金。显微组织分析、室温硬度测试、高温抗氧化性测试结果显示,两种耐磨硬质相大量析出并且均匀分布于合金中。与现役的高温耐磨材料相比,该合金同时具备高的室温硬度和1 050℃时优异的抗氧化性,有望成为新一代高温耐磨材料。     

一种Ni3Al基高温合金冷热疲劳性能研究北大核心

航空发动机叶片在服役时会经历反复升至高温又冷却的过程，这对于叶片材料Ni3Al基高温合金的抗冷热疲劳性能提出了较高的要求。本文对一种Ni3Al基高温合金进行了不同温度区间以及不同热循环次数对于裂纹产生及扩展的影响，并进行了不同周次的冷热循环试验。结果表明：冷热疲劳过程中，该Ni3Al基高温合金裂纹沿着共晶组织扩展，共晶含量的多少直接影响合金的抗冷热疲劳能力。在25℃■1 100℃下的抗冷热疲劳能力优于合金在2 5℃■1 150℃下的抗冷热疲劳能力。在25℃■1 100℃冷热疲劳裂纹长度与热循环次数是近似线性关系，其表达式为a=-1.22+0.233N。     

Ti3Al合金激光焊接接头高温拉伸性能及显微组织

研究Ti-24Al-17Nb合金激光焊接接头的室温及高温拉伸性能,并分析接头显微组织和拉伸断口。研究结果表明,室温下焊缝为单一β/B2相柱状晶组织,室温横向拉伸时接头强度与母材强度相当、塑性有所下降、但仍有25%左右的伸长率,断裂大部分发生在母材部位、少部分断裂在焊缝;高温拉伸时断裂均发生在焊缝部位。高温拉伸时,接头组织发生变化,α2相和B2相向O相转变;焊缝β/B2相向O相转变的切变相变,使原来柱状晶晶界应变集中、容易产生微裂纹,使接头高温强度和塑性明显降低,高温拉伸断口呈现沿晶断裂和解理断裂的脆性断裂形式。     

Microstructure/mechanical property relationship in a DS Cast Ni3Al-base alloy

A Ni-Al-Mo directionally solidified (DS) casting γ-base superalloy, with the chemical composition (wt%) 7.5 to 8.5% Ni, 10 to 14% Al, Mo ≤0.15% B, has been developed for advanced gas turbine blades and vanes. The mechanical properties of this alloy have been determined by tensile tests at room temperature and in the temperature range 700 to 1000 °C and by stress-rupture tests in the temperature range 760 to 1100 °C. The microstructures of the as-cast and homogenized specimens and of specimens after creep de-formation at 1000 to 1100 °C have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and optical microscopy techniques. The results show that this alloy has a high yield strength from room temperature up to 1100 °C, excellent creep resistance at temperatures up to 1100 °C, as well as a lower density and higher melting point than currently available nickel superal-loys. The microstructural observations and analysis indicate that the superior mechanical properties of this alloy may be attributed to solid solution hardening by the large molybdenum addition, second-phase strengthening by y phase and other minor phases that precipitate in various temperature ranges, the for-mation of a γ raft structure during creep, and to the existence of high-density misfit dislocation networks at γ / γ interface areas due to a high value of γ / γ misfit.     

Al含量对Ni3Al基IC10合金凝固行为的影响

研究Ni3Al基合金IC10两种不同Al含量合金中初生相的析出温度及析出顺序,确定了两种合金在不同等温温度下固-液两相比例变化。结果表明,低铝合金中(γ+γ′)共晶析出温度比高铝合金下降了20℃,液相线温度提高了5℃,并且失去枝晶间毛细补缩能力温度与固相线之间的温度范围明显缩小,失去枝晶间补缩区的液相量F明显减少,从而使低铝合金浇铸叶片时的热裂倾向降低,合金的可铸性提高。     

Microstructure and Properties of Ti_3Al-base Alloys

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不同钎料对Ti3Al基合金钎焊接头强度及界面微观组织的影响

研究了Ti3Al基合金真空钎焊及接头组织性能;分析了不同钎料对接头界面组织和剪切强度的影响,初步优选了钎料,优化了钎焊连接规范参数;利用电子探针、扫描电镜和X射线衍射等方法对接头进行了定性和定量分析.结果表明:采用NiCrSiB钎料连接时,在界面处有金属间化合物TiAl3、AlNi2Ti和Ni基固溶体生成,TiAl3和AlNi2Ti的生成降低了接头的剪切强度;采用TiZrNiCu钎料连接时,在界面处有金属间化合物Ti2Ni、Ti(Cu,Al)2和Ti基固溶体生成,Ti2Ni和Ti(Cu,Al)2的形成降低了接头的剪切强度;采用AgCuZn钎料连接时,在界面处生成TiCu、Ti(Cu,Al)2和Ag基固溶体,TiCu和Ti(Cu,Al)2的生成是降低接头剪切强度的主要原因;采用CuP钎料连接时,在界面处生成了Cu3P、TiCu和Cu基固溶体,CuaP和TiCu使接头的剪切强度降低;对于NiCrSiB钎料,当连接温度为1 373 K,连接时间为5 min时,接头的剪切强度最高为219.6 MPa对于TiZr-NiCu钎料,当连接温度为1 323 K,连接时间为5 min时,接头的最高剪切强度为259.6 MPa;对于AgCuZn钎料,当连接温度为1 173 K,连接时间为5 min时,接头的最高剪切强度为125.4 MPa;对于CuP钎料,当连接温度为1 223 K,连接时间为5 min时,接头的最高剪切强度为98.6 MPa;采用TiZrNiCu钎料连接Ti3Al可获得最大接头强度.     

Microstructures and properties of transient liquid phase diffusion bonded joints of Ni_3Al-base superalloy

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Room temperature tensile deformation behavior of a Ni-based superalloy with high W content

K416B Ni-based superalloy with high W content has good high temperature properties and low cost, which has a great development potential. To investigate the room temperature tensile property and the deformation feature of K416B superalloy, tensile testing at room temperature was carried out, and optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the deformation and damage mechanisms. Results show that the main room temperature tensile deformation features of the K416B nickel-based superalloy are dislocations slipping in the matrix and shearing into γ′ phase. The <110> super-dislocations shearing into γ′ phase can form the anti-phase boundary two coupled (a/2)<110> partial-dislocations or decompose into the configuration of two (a/3)<112> partial dislocations plus stacking fault. In the later stage of tensile testing, the slip-lines with different orientations are activated in the grain, causing the stress concentration in the regions of block carbide or the porosity, and cracks initiate and propagate along these regions.

     

Microstructure of model cermets with high Mo or W content

The microstructure of (mol%) TiC–18TiN–24Ni–(10–29)WC and TiC–18TiN–24Ni–(5–14)Mo₂C has been investigated using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and analytical electron microscopy (AEM). When the WC content in the raw materials was increased the W content in the outer rim of (Ti, W)(C, N) grains increased until it had a composition similar to that of the inner rim. If the WC content was high undissolved WC was present after sintering. When the Mo₂C content in the raw materials was increased, the volume fraction of inner rim increased and the Mo content in both inner and outer rim increased. Thermodynamical calculations on the Ti–W–C–N system suggest that the inner rim is formed during solid state sintering when there is an open porosity and thus a low nitrogen activity. The composition of the outer rim can be explained by the equilibrium at the sintering temperature if the volume fraction of undissolved Ti(C, N) cores is subtracted. Calculations on the Ti–Mo–C–N system show that (Ti, Mo)(C, N) decomposes into two phases with different Mo content and that the Ti(C, N) cores might be regarded as a stable phase.     

Microstructure and microhardness of Co-8.8Al-9.8W superalloy cladding layer with different boron content

TIG welding was used to deposit Co-8.8 Al-9.8 W-0.2 B superalloy on 304 austenite stainless steel. The form factor of weld, dilution ratio, microhardness, microstructure and distribution of alloying elements were investigated. The microstructure of cladding layer was mainly hypoeutectic. The primary phases were cobalt-rich solid solution. The eutectic phase was composed of cobalt-rich solid solution,Co6W6C and Co Cx. When the boron content increased from 0.2% to 0.5%,the dilution ratio decreased,the primary phase became coarse and the microhardness decreased. When the boron content was from 0.5% to 2%,the dilution ratio and microhardness increased obviously,but the primary phase was refined.The hard phase of Co-8.8 Al-9.8 W became refined and the amount was raised,and the performance of cladding layer was improved with appropriate boron increase.