新型细化剂对K4169高温合金微观组织的影响

研究了新型晶粒细化剂对K4169高温合金枝晶组织、元素显微偏析和合金相的影响。实验结果表明：在同一浇注温度下，细晶铸造试样的一次枝晶主轴长度较普通铸造试样明显缩短，但二者的二次枝晶臂距没有显著差别。晶粒细化后，晶粒的形态由普通铸造组织中的树枝晶向细晶组织中的粒状晶转变，而反合金中主要元素Fe、Cr、Nb、Mo和Ti的偏析减轻，这些均有利于提高细晶铸件的机械性能。另外，MC型碳化物和Laves相的尺寸、数量和形貌在晶粒细化前后变化不大。     

新型细化剂对K4169高温合金晶粒组织的影响

研究了新型细化剂对K4169高温合金晶粒组织的影响，提出了晶粒细化的机理。结果表明：加入新型细化剂不仅使凝固后基体的晶粒尺寸减小，而且可提高铸件断面等轴晶的比例。在通常浇注温度1400℃下，加入由两种三元金属间化合物所制成的复合细化剂，对合金熔体进行、不进行均匀化处理时，可使圆柱锭的晶粒分别细化至ASTM1．7级和ASTM3．2级；断面等轴晶的比例从56％分别提高到96％和99％。研究还发现细化剂加入工艺如加入单一或复合细化剂、细化剂的种类和粒度等的不同会产生不同的细化效果，本对这些现象进行了解释。     

定向凝固工艺下大尺寸DSM11铸件的显微组织

为了实现液态金属冷却法（LMC）的工程化应用,研究了传统高速凝固法（HRS）和液态金属冷却法两种定向凝固工艺下得到的大尺寸DSM11合金铸件的显微组织.结果表明,与HRS工艺相比,LMC工艺得到的大尺寸铸件组织更均匀,一次、二次枝晶间距小,三次枝晶不明显,共晶尺寸小、含量少,缩孔等缺陷少,枝晶干和枝晶间的γ′尺寸小、差别小,碳化物细小且分布均匀.此外,LMC工艺使合金元素微观偏析减小,抑制了块状η相析出倾向.     

Mg-Al4C3中间合金对AZ31B镁合金组织的细化

采用SEM、EDS 和XRD 等测试手段研究Mg-50%Al4C3中间合金对AZ31B 镁合金显微组织的细化效果.研究结果表明,中间合金的加入可显著细化AZ31B镁合金的枝晶组织和晶粒尺寸.当Al4C3的加入量为0.9%时,α-Mg 晶粒的平均尺寸由基体合金的280 μm降至约53 μm.β相由连续网状转变为不连续的网状和细小弥散的粒状.通过能谱分析及面错配度计算证实,Al4C3可成为初生α-Mg晶粒的良好异质核心.     

镍铁基合金表面激光熔覆层的显微组织及耐磨性能

对光纤作用下的镍铁基合金表面熔覆层的显微组织及耐磨性能进行研究.结果表明,用微米尺度的混合粉末作为熔覆粉末制备的涂层表面无气孔和明显裂纹等缺陷,显微组织主要是细小的枝晶、柱状晶和胞状晶;添加碳化物VC和Cr_3C_2有助于改善涂层组织的均匀性,细化晶粒尺寸;与母材对比,涂层的耐磨性能显著提高.     

RE、Sr变质对AHS-2铝合金组织及性能的影响

研究了RE、Sr、RE+Sr不同变质处理AHS-2铝合金铸态显微组织变化.实验结果表明:当RE0.1%+Sr0.3%复合变质AHS-2合金时,其组织中的初生α-Al发生明显细化,形貌呈细小圆球状等轴晶,尺寸约为20~30μm,且分布均匀,共晶硅晶粒细小,合金得到良好的变质细化效果.     

挤压工艺对AK4—14合金棒材晶粒大小的影响

通过调整合金成分分别配制了添加Zr,AlTiB,AlTiC和RE的AK4-14,实验铝合金,经过2种不同的工艺生产棒材,在室温下测量其淬火时效态抗拉强度,用金相显微镜和扫描电镜观察和分析了合金在不同加工工艺状态下的显微组织和结构,并判定其晶粒度,结果表明：在设计合金成分时,要精确控制Cu的含量在2．0％－2．6％,以免发生难溶的含Cu相,降低合金的强度;多向强应变可细化晶粒,提高合金的力学性能;随变形程度的增加,晶粒尺寸减小;制定挤压工艺时,为避免产生周期性裂纹,建议挤压比取为25左右。     

Gd对ZK60镁合金显微组织的影响

采用光学金相显微镜、扫描电镜、能谱分析等方法研究了ZK60-xGd(x=0,1.6,2.0)合金的铸态和热挤压态显微组织.研究发现,ZK60合金铸态组织主要由α-Mg枝晶和分布在其周围的半连续网状或不规则片状MgZn相和颗粒状MgZn_2相组成.加入Gd后,MgZn相变为细小均匀的颗粒状,并且随着Gd含量的增加,α-Mg枝晶细化程度和颗粒相分布均匀度提高.Gd在热挤压过程中诱发了合金动态再结晶的进行,显著地细化ZK60-xGd合金挤压态晶粒尺寸,细化程度随着Gd含量的增加而显著提高.结果表明Gd能够显著地细化ZK60铸态和挤压态晶粒,有利于形变镁合金ZK60的变形.     

含稀土Er的Al-Zn-Mg合金的组织与性能

为了探讨稀土Er对热处理可强化(沉淀强化)的铝合金系作用,采用铸锭冶金法制备了6种含Er量不同的Al-Zn-Mg合金进行了深入分析.通过硬度测试、拉伸力学性能测试、金相观察、X射线衍射和扫描电镜观察,研究了稀土元素Er对Al-Zn-Mg合金显微组织和力学性能的影响.实验结果表明,稀土元素Er可以显著地细化Al-Zn-Mg合金的铸态晶粒,减小其枝晶网胞,当Er的添加量达到w(Er)=0.7％时,枝晶网胞几乎完全消失,晶粒变得非常细小且分布均匀;对于合金的冷轧态组织以及时效态晶粒也有同样的细化效果;添加Er后,Al-Zn-Mg合金在冷轧态及时效态下的屈服强度(σ0.2)及抗拉强度(σh)都得到了显著的提高,但塑性有所降低;稀土元素Er添加到Al-Zn-Mg合金中,主要与Al相互作用形成了Al3Er相.合金显微组织的细化及合金的强化都与该相的形成和析出有关.     

Si对K40S合金凝固过程及显微组织的影响

研究了Si对K40S合金凝固过程及显微组织的影响。结果表明,随着Si含量的升高,K40S合金凝固时界面生长由枝晶生长转向明显的内生生长;Si元素主要在枝晶间或晶界偏析,但当Si含量升高到一定程度后,枝晶内的浓度逐步升高而达到显著水平;Si元素对合金中Cr、Ni、W等元素的分布有影响,进而影响碳化物的形成。     

Grain Refining Performance of SHS Al—50TiC Master Alloys for Commercially pure Aluminum

An Al-50wt^TiC composite was directly synthesized by self-propagating high-temperature synthesis(SHS) technology,and then was used as a grain refining master alloy for commercially pure aluminun.The microstructure and grain refining performance of the synthesized master alloy were emphatically investigated.The SHS master alloy only ocntained submicron TiC particles except for Al matrix.Moreover,TiC particles were relatively free of agglomeration.Grain refining tests show that adding only 0.1wt^ of the master alloys to the aluminum melt could transform the sturcture of the solidified samples from coarse columnar grains to fine almost 1.5h at 1003K.Therefore,it is concluded that the SHS master alloy is an effective grain refiner for aluminum and its alloys,and that it is highly resistant to the grain refining fading encountered with most grain refiners.     

Study on Grain Refining and Metamorphism of ZL111 Aluminium Alloys

Vacuum sintering and ball milling methods were employed in the preparation process of Ti-C grain refinement and the ability of refiners with varying ratios of Ti and C to refine ZL111 crystal grains was tested. The refinement effect of the Ti-C ratios on tensile strength, elongation percentage, Brinell hardness, pro-eutectoid αAl and the size of the Si phase of ZL111, after modification by rare-earth and strontium nitrate, were studied by means of metallographic examination, SEM and mechanical property tests. The results show that there is an obvious increase in the tensile strength and elongation percentage of refined ZL111 with these new Ti and C refiner compounding powders, while Brinell hardness remained more or less constant. The pro-eutectoid αAl is considerably reduced in size and the Si phase shows a finer and rounder structure. The refiner exhibits a good grain refining performance when the Ti-C ratio is 25：1, for Al crystals can favorably easily form nuclei and grow up along the TiC surface thanks to the TiAl3 generated by surplus Ti and Al. The mechanical properties have clearly been improved by the addition of strontium nitrate to ZL111. The effective factors in the modification of mechanical properties of ZL111 are in order of importance： strontium nitrate, Ti-C ratio and rare earth.     

Semi-solid casting of high speed steel ingots using inclined slope pre-crystallization method

Semi-solid casting of M2 high speed steel ingots was investigated by inclined slope pre-crystallization method. Effects of casting temperature and slope length on the microstructure of M2 HSS ingots were investigated. M2 cast ingots of non-dendritic primary austenite and fine eutectic ledeburite network carbide structure were obtained, with the casting temperature, slope length and angle of 1480 °C, 500 mm and 60° respectively. Meanwhile, the microstructure of cast samples was quantitatively assessed by Image tool software. Results show that optimum mean equivalent diameter of primary austenite crystal grain is 50.8 μm, shape factor is 0.83, and mean thickness of network carbide is 5.21 μm.     

Effect of solution cooling rate on the γ′ precipitation behaviors of a Ni-base P/M superalloy

The effect of cooling rate on the cooling γ′ precipitation behaviors was investigated in a Ni-base powder/metallurgy (P/M) superalloy (FGH4096). The empirical equations were established between the cooling rate and the average sizes of secondary and tertiary γ′ precipitates within grains and tertiary γ′ precipitates at grain boundaries, as well as the apparent width of grain boundaries. The results show that the average sizes of secondary or tertiary γ′ precipitates are inversely correlated with the cooling rate. The shape of secondary γ′ precipitates within grains changes from butterfly-like to spherical with the increase of cooling rate, but all the tertiary γ′ precipitates formed are spherical in shape. It is also found that tertiary γ′ may be precipitated in the latter part of the cooling cycle only if the cooling rate is not faster than 4.3°C/s, and the apparent width of grain boundaries decreases linearly with the increase of cooling rate.     

电热爆炸喷涂法制备TiC涂层的特性分析

采用电热爆炸定向喷涂工艺在镍合金基体上制备TiC涂层,借助光学显微镜、显微硬度计分别对涂层显微组织、涂层硬度进行了测试。利用图像分析软件对涂层的晶粒尺寸进行了测量。结果表明,电热爆炸定向喷涂制备的涂层组织晶粒明显细化,涂层组织为典型的快速凝固组织。涂层组织比原始喷涂材料镍合金组织细小、均匀;TiC涂层中大晶粒所占涂层面积为93.6%,小晶粒所占面积为6.4%;大晶粒的弦长平均值为500 nm左右,小晶粒的弦长平均值为81 nm左右;表层有些孔隙;涂层硬度均明显高于基体材料镍合金的硬度,其最高硬度达到了582.5 HV。     

稀土Dy、退火对Dyx(Co40Ag60)100-x颗粒膜的结构与巨磁电阻效应的影响

采用磁控溅射法制备了Dyx(Co40Ag60)100-x颗粒膜.X射线衍射实验结果表明,Dyx(Co40Ag60)100-x颗粒膜的晶体结构具有一定的择优取向,退火温度升高能够促进这种择优取向并加速Ag颗粒的聚集生长和Ag中的Co发生相分离;稀土元素Dy起到细化晶粒的作用,并且阻碍晶面择优取向的进程,导致薄膜结构中的晶...     

钢金相图像中晶粒度的估算方法

晶粒度估算是金属性能分析的重要基础。对钢金相图像中晶粒的晶粒度、面积、平均面积、弦、长轴、短轴、直径和平均直径进行了定义,提出用填充剔除计数法进行晶粒颗数的统计,给出了一个晶粒平均面积和平均直径的估算公式。最后,给出了一个晶粒直径计算算法。描述的晶粒度估算方法改进了从前的粗略估算方法,使计算精确度获得极大的提高,为金相图像的更深入分析,如对金属晶粒度的评级、机械性质的分析等提供了很大的帮助。     

煤矸石固结压密性与 颗粒级配缺陷关系研究

重点探讨了煤矸石粒度分布的级配与压密性的关系问题,用不同颗粒级配煤矸石所作的压密和渗透对比试验的结果表明,影响天然煤矸石固结压密性的主要级配缺陷是细小颗粒含量比例过低,通过适当提高矸石中细小颗粒含量的级配改良,不但可以有效提高煤矸石的固结性,使其在较低的压密能量下取得较高的固结压密程度,并且能够使煤矸石的水稳性得到明显改善.     

Formation of bulk ferromagnetic nanostructured Fe<Subscript>40</Subscript>Ni<Subscript>40</Subscript>P<Subscript>14</Subscript>B<Subscript>6</Subscript> alloys by metastable liquid spinodal decomposition

Nanostructured Fe₄₀Ni₄₀P₁₄B₆ alloy ingots of 3–5 mm in diameter could be synthesized by a metastable liquid state spinodal decomposition method. For undercooling ΔT > 260 K, the microstructure of the undercooled specimen had exhibited liquid state spinodal decomposition in the undercooled liquid state. The microstructure could be described as two intertwining networks with small grains dispersed in them. For undercooling ΔT > 290 K, the overall microstructure of the specimen changed into a granular morphology. The average grain sizes of the small and large grains are ≅ 30 nm and ≅ 80 nm, respectively. These prepared samples are soft magnets with saturation magnetization B _s ≅ 0.744 T. Supported by the Hong Kong Research Grants Council the National Natural Science Foundation of China (Grant No. 50861007) and Xinjiang University Doctoral Research Start-up Grant (Grant No. BS050102)