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1.
研究新型颗粒细化剂COVERAL MTS 1582对A356铝合金的细化效果。结果表明,经过COVERAL MTS 1582颗粒细化剂处理后,A356铝合金的铸态组织较添加传统细化剂Al-5Ti-B处理的二次枝晶间距(26.9μm)减小约23.8%。说明该新型颗粒细化剂对A356铝合金比Al-5Ti-B具有更显著的细化作用,同时,该新型颗粒细化剂的加入量低,可减少细化剂的使用量,且生成的铝渣含铝量少,降低处理成本。  相似文献   
2.
Improving the piezoelectric activity of lead zirconate titanate (PZT) ceramics is of great importance for practical applications. In this study, the influence of Pr3+ doping on the ferroelectric phase composition, microstructure, and electric properties on the A-site of (Pb1-1.5xPrx)(Zr0.52Ti0.48)O3 is extensively investigated. A dense and fine microstructural sample is obtained with the introduction of Pr3+. The results show that the morphotropic phase boundary (MPB) moves to the rhombohedral phase region. The rhombohedral and tetragonal phases exhibit an ideal coexistence in the 4 mol.% Pr3+ doped (PPZT4) samples. Lead vacancy and the reduction of the potential energy barrier are considered to be the key mechanisms for donor doping, which is upheld by the Pr3+ doping. Combining the I-E hysteresis loops with the P-E hysteresis loops, it becomes apparent that both contribution maximums of the domain switching and residual polarisation are in PPZT4. Moreover, the thermal aging resistance of PZT is improved by doping, and the temperature stability is optimised from 83% in PZT to 96% in PPZT4. Hence, an appropriate amount of Pr3+ doping can effectively improve the piezoelectric activity of PZT ceramics in the MPB area and optimise the performance stability of the material under application temperatures.  相似文献   
3.
The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate some δ phases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT tem-perature is 980℃.The phenomenon attributes to the uneven distribution of δ phase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number of δ phases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with few δ phases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prereq-uisite to precipitate even-distributed δ phase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation around δ phase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).  相似文献   
4.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB2and(1-100)NbB2surface can be substituted by Al to form(Al,Nb)B2intermedia layers.In addition,a layer of NbAl3-like compound(NbAl3')can cover the surface of NbB2with the orientation relation of(1-100)[11-20]NbB2//(110)[110]NbAl3'.Both of the(Al,Nb)B2and NbAl3'intermedia layers contribute to enhancing the nucleation potency of NbB2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys.  相似文献   
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6.
本文以医疗器械行业常用材料纯镁丝为研究对象,采用一种新型大塑性多道次转角拉拔(M-PAD)变形工艺,建立了M-PAD变形模型,并模拟了拉拔过程中纯镁材的等效应力、等效应变变化图;通过设计便于进行拆卸与实验操作的M-PAD模具,对纯镁M-PAD变形工艺参数进行了试验研究。结果表明:M-PAD拉拔变形有利于晶粒的均匀细化,在第1次拉拔后,试样的晶粒得到细化,拉拔2次后晶粒大小无明显变化;M-PAD拉拔过程应选取合适的参数,本次试验得出的最优拉拔参数为4 mm/min速度下进行2次M-PAD拉拔。  相似文献   
7.
将Al-5Mg-0.18Mn-0.2Sc-0.08Zr-0.01Fe-0.01Si(质量分数,%)合金铸锭进行多向等温锻造(应变12)或等径角挤压(应变10,325℃),再进行热轧(325℃)和冷轧(20℃),对比研究合金变形后的组织和力学行为。结果表明,对(亚)晶粒尺寸dUFG=2μm的超细晶组织合金进行多向等温锻造后,其室温延展性提高,超塑性伸长率可达2800%。通过热轧进一步细化晶粒,后续再通过冷轧形成高位错密度的严重变形组织,合金的屈服/极限抗拉强度从多向等温锻造后的235/360 MPa分别提高到热轧和冷轧后的315/460 MPa和400/515 MPa。同时,热轧使超塑性伸长率提高到4000%,而冷轧后的伸长率仍然足够高(高达1500%)。与多向等温锻造相比,经等径角挤压后合金的晶粒细化程度更高(dUFG=1μm),强度和超塑性性能均得到提高。然而,热轧后此效果有所减弱,加工后的板材具有同等的性能。与多向等温锻造后再冷轧的合金相比,经等径角挤压后再冷轧的合金强度更高,超塑性性能略好。  相似文献   
8.
采用OM、SEM以及硬度测试等方法研究了淬火工艺中冷却速率对过共析轨钢珠光体组织特征的影响规律。结果表明,随着冷却速率的提高,珠光体片层间距和渗碳体厚度均逐渐减小,分别由302 nm和43.6 nm减小到205 nm和29.2 nm。珠光体片层间距的细化对硬度提高起到了一定作用,使其由286 HV提高到了348 HV。  相似文献   
9.

This work aims to produce a high manganese steel with more refined austenite grains and better wear resistance without sacrificing the toughness and tensile properties by Mn alloying and Ti ladle treatment in comparision to ASTM A128 Gr. E1 steel (1.0C-13Mn) that is mostly used in the mining industry. The 1.0C-17Mn-xTi alloys (x=0, 0.05 and 0.1, in wt.%) were prepared. A relationship was established between the microstructures and mechanical properties of the as-cast and solution annealed alloys. Increasing Ti content increases the stable Ti(CN) phase on and beside the grain boundaries and decreases up to 37% the austenite grain size of the as-cast alloy with 0.10wt.% Ti. Correspondingly, after solution annealed, optimized titanium content (0.05wt.%) results in significant improvements in wear resistance, hardness, elongation, yield and tensile strengths by 44%, 31%, 30%, 8% and 12%, respectively, except 9% decrease in impact toughness compared to ASTM A 128 Gr. E1 steel without modification. These results show that 1.0C-17Mn-0.05Ti alloy can be used for parts exposed to high load wear and applied in conditions where relatively high tensile properties with sufficent ductility is needed.

  相似文献   
10.
张翠翠  吴化  于晓丰 《表面技术》2021,50(5):315-320
目的 利用搅拌摩擦加工技术制备纳米SiC铝基复合材料,研究经过纳米粒子的添加和FSP作用后,其耐腐蚀性能的变化及原因.方法 室温条件下,在3.5%NaCl溶液中,通过电化学阻抗谱和动电位极化曲线对试样的耐腐蚀性能进行检测分析.利用电子背散射衍射技术和透射电镜对3种试样的显微组织进行表征,研究耐腐蚀性能的变化机理.结果 经搅拌摩擦加工后,样品的阻抗值明显提高,动电位极化曲线测试结果显示,母材、FSP试样和复合材料试样的自腐蚀电位分别为–1.517、–1.338、–1.339 V,而腐蚀电流密度分别为0.48、0.11、0.12 mA/cm2.FSP加工试样的晶粒由平均晶粒尺寸为8.7μm左右的等轴晶粒构成,并且大部分析出相因高温作用发生溶解,而纳米SiC粒子的加入,使晶粒尺寸进一步降低至4.1μm左右.结论 所制备Al6061/SiC复合材料的耐腐蚀性能相较于母材明显改善,但弱于FSP试样.SiC和基体之间电位差的存在构成腐蚀微电池,降低材料的耐腐蚀性能,而晶界数量的增加造成点阵空位等缺陷增加,导致电荷转移的阻力增加,耐腐蚀性能得到改善.  相似文献   
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