Altered age-hardening behavior in the ultrafine-grained surface layer of Mg-Zn-Y-Ce-Zr alloy processed by sliding friction treatment

To gain insight into the ageing behavior of ultrafine grain(UFG)structure,the precipitation phenom-ena and microstructural evolutions of Mg-6Zn-1Y-0.4Ce-0.5 Zr(wt.％)alloy processed by sliding friction treatment(SFT)were systematically studied using hardness texting,transmission electron microscopy(TEM)equipped with high-angle annular dark-field scanning(HADDF-STEM),X-ray diffraction(XRD)and XRD line broadening analysis.The microhardness of the SFT-processed(SFTed)sample initially decreases from 109.6 HV to 104.8 HV at ageing for 8 h,and then increases to the peak-ageing point of 115.4 HV at 16 h.Subsequently,it enters the over-aged period.The un-SFTed sample,as the counterpart,follows a regular ageing behavior that increases from 89.9 HV to 99.6 HV when ageing for 12 h,and then drops.A multi-mechanistic model is established to describe the strengthening due to grain refinement,disloca-tion accumulation,precipitation etc.The analysis reveals that the temperature sensitive UFG structure has an obvious grain coarsening effect,which arouses the soft phenomenon in the early ageing stage.But precipitation hardening provides an excellent hardness enhancement for overcoming the negative influ-ence and helping to reach the peak-aged point.In our microstructural observations,a lot of equilibrium ultrafine MgZn2 precipitates precipitate along dislocations because defects can provide the favorable conditions for the migration and segregation of solute atoms.     

强变形工艺对2519A铝合金组织与性能的影响

通过硬度测试、拉伸性能测试、透射电镜观察等分析手段研究了不同强变形工艺下2519A铝合金的力学性能与微观组织。结果表明,经50%的冷轧变形和165 ℃人工时效后,2519A合金的力学性能明显提高,其抗拉强度、屈服强度和伸长率分别为522 MPa、468 MPa和8.5%。而在冷变形前添加165 ℃×2 h预时效处理,合金的力学性能进一步提高,其抗拉强度、屈服强度和伸长率分别达到535 MPa、497 MPa和8%。预时效处理可以提高合金中θ′相的密度,使析出相分布更加均匀,有助于提高合金的力学性能。     

纳米结构9Cr-ODS钢的制备工艺

本文对利用雾化法直接制备出Y、Ti过饱和固溶的粉体合金,经短时机械合金化和热等静压成型制备纳米结构9Cr-ODS钢技术进行了研究.采用扫描电镜和X射线衍射研究雾化合金粉与短时球磨后雾化合金粉的形貌特征与组织的演化.通过高分辨透射电镜和电子背散射衍射研究热固化成型后ODS钢的微观组织.测试了雾化粉和球磨8 h合金粉热固化成型样品的应力-应变曲线.结果表明,用短时球磨雾化粉制备的ODS钢晶粒尺寸更加细小、形成高密度纳米尺寸的析出相.与常规方法制备的ODS钢相比,抗拉强度略高、塑性显著提高、球磨时间大幅缩短.     

含复合(Ti,Mo)C析出相的马氏体钢的氢捕获与解吸附

采用热脱氢分析装置 (TDS) 研究了含复合 (Ti,Mo)C析出相的马氏体钢的氢的捕获与解吸附行为。结果表明,36-60 nm的未溶球形(Ti,Mo)复合析出相在室温电化学充氢过程中不能捕获氢,而回火析出的1-5 nm的复合 (Ti,Mo)C析出相是有效的氢陷阱,尽管其氢陷阱激活能相对较低,为16.4-22.1 kJ/mol,与晶界、位错处的氢陷阱激活能相近,同时远低于纯的共格TiC析出相的氢陷阱激活能,但在大气中放置时,被回火析出的1-5 nm的复合 (Ti,Mo)C析出相捕获的氢无法解吸。     

固溶处理对节镍型2101双相不锈钢组织及力学性能的影响

采用光学显微镜、透射电镜和X射线衍射等研究了固溶处理对2101节镍型双相不锈钢连铸坯边部试样的组织、相比例和力学性能的影响。结果表明:在1050~1150℃固溶处理时,双相不锈钢具有很好的高温塑性;在1000~1150℃温度范围,随着温度的升高,实验钢的断面收缩率和铁素体相比例先减小后增加;随着固溶温度增加,实验钢的抗拉强度逐渐降低,但在1050℃时有所增加,这是由于在此温度固溶过程中,铸态试样相界处Cr2N析出相完全溶解,使得大量的N原子集中在相界处,促进了相界附近的铁素体相发生相变,转变成奥氏体相,导致在此1050℃时实验钢铁素体相的比例减小,断面收缩率减小,抗拉强度增加。     

Effect of pH on the detailed chemical nature and metal-carbonate species in as synthesized zirconia alumina composites

Zirconia was deposition precipitated on γ-alumina in pH range 7-10 from zirconium oxy-nitrate and soda ash. Zirconium formed its hydroxycarbonate as deduced from ICP-EOS, CHN, and TGA-MS. Higher pH favored formation of carbonate species of zirconium over its hydroxide. TGA-MS indicated formation of three different types of carbonate species. FTIR results corroborated this. Monodentate metal carbonate was observed irrespective of pH of preparation. In addition, bridged bidentate species formed at pH ≤ 8 which changed to chelating bidentate at pH > 8. XRD indicated that all the samples formed tetragonal-zirconia upon calcination irrespective of pH of preparation. Higher pH resulted in smaller crystallites of t-ZrO₂. Changes in chemical moiety with pH reflected on acidity and the deactivation rate for 2-methyl-3-butyn-2-ol which decreased by two orders of magnitude in samples prepared at higher pH. Surface area and pore volume benefited from deposition precipitation. SEM-EDAX showed reasonable distribution of zirconia over γ-Al₂O₃.     

道次压下量对2197铝锂合金轧制组织与力学性能的影响

针对铝锂合金塑韧性、成形性差的问题,本工作通过OM/SEM微观组织分析、拉伸及硬度/电导率测试,研究了在总压下量75%条件下、轧制道次压下量(即10%、30%、30%+60%,分别对应小、中、大道次压下量)对2197铝锂合金组织与力学性能的影响。结果表明：道次压下量显著影响铝锂合金的晶粒结构、析出相的数量及分布。轧制态合金的强度随单道次轧制压下量的增加而显著增加、而塑韧性则明显下降。T8时效处理使析出相大量析出,轧制合金中的Portevin-Le Chatelier(PLC)效应得到消除,小、大道次压下量轧制合金的力学性能得到显著提升。大压下量轧制合金经时效处理后强塑性综合力学性能最高,抗拉强度为384.94 MPa、断后伸长率为12.45%,较小、中道次压下量轧制时效合金分别提高2%、21%和29%、31%。