The Influence of Hot-Rolled Temperature on Plasma Nitriding Behavior of Iron-Based Alloys

Experiments were performed with an aim of studying the effect of hot-rolled temperature (600 and 900°C) on radio frequency (rf) plasma nitriding of Fe₉₃Ni₄Zr₃ alloy. Nitriding was carried out for 10 min in a nitrogen atmosphere at a base pressure of 10^?2 mbarr. Different continuous plasma processing powers of 300–550 W in steps 50 W or less were applied. Nitrided hot-rolled specimens were characterized by optical microscopy (OM), X-ray diffraction (XRD) and microhardness measurements. The results reveal that the surface of hot-rolled rf plasma nitrided specimens at 600°C is characterized with a fine microstructure as a result of the high nitrogen solubility and diffusivity. Moreover, the hot-rolled treated samples at 600°C exhibit higher microhardness value than the associated values of hot-rolled treated samples at 900°C. The enhancement of microhardness is due to precipitation and predominance of new phases (γ and ε phases). Mainly, this conclusion has been attributed to the high defect densities and small grain sizes of the samples hot-rolled at 600°C. Generally, the refinement of grain size plays a dramatic role in improvement of mechanical properties of tested samples.     

块体非晶态合金的疲劳性能与超塑性变形

综述了块体非晶态合金的疲劳性能以及过冷液相区的超塑性变形行为及其研究进展,最后简要论述了尚需进一步研究的问题及今后的发展趋势.     

非晶态合金的局域剪切变形与断裂机制

从自由体积模型、绝热剪切模型、位错模型及力学模型等方面全面综述了非晶态合金的局域剪切变形与断裂机制,提出了“自由体积＋绝热升温”模型并解释了合金的变形与断裂过程,最后简要讨论了该领域目前存在的问题及今后的发展趋势。     

镁合金塑性变形力学行为与微观组织研究进展

介绍了镁合金在单轴压缩、单轴拉伸、轧制和挤压条件下塑性变形的力学行为及微观组织结构演变规律。简述了镁合金中二次拉伸孪生现象以及各种变形条件下孪生与孪生变体类型的选择规律。基于对镁合金位错滑移、机械孪生及动态回复与再结晶行为的认识,对镁合金力学行为的各向异性、轧制与挤压成型能力的影响规律进行了探讨,强调了初始织构对变形机制、动态再结晶及成型能力的重要影响。最后讨论了析出强化镁合金塑性变形与强韧化机理。     

Ti-Al-Nb合金的热变形与动态再结晶行为研究

目的 建立本构方程及动态再结晶模型,描述热变形条件对Ti-Al-Nb合金动态再结晶以及合金软化的影响规律。方法 基于热模拟压缩变形试验,获得Ti-Al-Nb系合金在不同热变形工艺参数下的应力应变曲线。采用双曲正弦模型表征流动应力,通过线性回归等数据处理方式求得各参数的具体数值。结果 求得动态再结晶活化能Q=197.626 kJ/mol,材料常数A的平均值为3.173×10⁶,建立流动应力本构方程。Z/A为无量纲参数,通过最小二乘线性拟合求得ε^*=344×10⁵(Z/A)^0.495,εc=16.15(Z/A)^0.24。结论 Ti-Al-Nb系合金在峰值应力出现之前均发生了动态再结晶:当应变速率较高时,在流动稳定前会发生强烈的软化,曲线显现双峰;当应变速率较低时,在加工硬化和软化作用达到平衡后逐渐进入稳定阶段,此时曲线显现单峰。研究结果将为Ti-Al-Nb系合金的精密塑性成形提供一定的技术参考和理论依据。     

ZT3非晶合金在过冷液相区的塑性变形研究

目的 研究不同的应变速率和变形温度对Zr30.2Ti32.9Cu9Ni5.3Be22.6非晶合金(亦称ZT3)在过冷液相区塑性变形行为的影响。方法 首先,用真空非自耗电弧炉熔炼合金锭并吸铸成直径为8 mm、长度为60~80 mm的非晶合金圆棒;然后,通过等温晶化试验确定ZT3非晶合金在过冷液相区中对应不同温度时发生晶化转变所需的最短时间,并用热模拟试验机进行压缩变形的试验研究;最后,用X射线衍射仪测试ZT3非晶合金在过冷液相区塑性变形后的组织特性。结果 ZT3非晶合金在过冷液相区内的塑形变形行为与应变速率和变形温度有密切的关联性。不同的应变速率与变形温度都会对其塑性变形产生影响,但变形温度的影响比恒定应变速率更大。对ZT3非晶合金变形后的结构分析发现,应变速率对非晶态结构的影响大于温度。结论 ZT3非晶合金的等温晶化转变孕育时间最短为17 min,在小于17 min的时间内完成塑性变形即可抑制晶化转变的发生。当恒定应变速率为2×10^?3 s^?1时,将变形温度控制在355~375 ℃范围内有利于ZT3非晶合金在过冷液相区进行热压塑性成形。     

凝固条件对非晶合金的微观结构和性能的影响

采用不同凝固控制的方法,研究了凝固条件对非晶合金的微观结构、热稳定性以及力学性能的影响。研究表明,高温下铜模喷铸样品为完全非晶结构,而低温喷铸和电弧原位吸铸所制备的样品中存在着一些纳米量级的析出相。高温喷铸样品表现出非晶合金典型的脆断行为,但低温喷铸和原位电弧吸铸样品则表现出较高的强度和良好的塑性变形能力。高温甩带样品初始晶化温度高于相应的低温甩带样品,其长期热稳定性优于低温甩带样品,表明浇铸温度的升高增强了非晶合金的热稳定性。     

Influence of Alloy Elements on Magnetic Properties of Fe-based Amorphous Alloys

1. IntroductionThe Fe-based amorphous alloy is a kind of important soft magnetic materials. Fe-St-B system amorphous alloys containing about 80 at. pci Fe havethe highest saturation magnetization induction. Thereseachers in the world pay a great attention to it.In order to enhance some magnetic properties to satisfy the demand of the different applications, the alloy compositions and the technological processes wereinvestigatedll~4]. In this article, the effect of alloy elements on the magne…     

热处理温度对非晶合金耐蚀性能的影响

目的 在非晶合金过冷液相区范围内研究热处理温度对非晶合金耐蚀性能的影响。方法 采用差示扫描量热法来表征非晶合金,并作出非晶合金的差热曲线,以此来确定非晶合金的玻璃化转变温度Tg和晶化温度Tx,进而求出其过冷液相区范围,以此来确定热处理退火温度范围。随后在过冷液相区范围内均匀选取3个不同温度点对非晶合金进行热处理,最后在质量分数为3.5%的NaCl溶液中对非晶合金进行电化学测试,并与未处理样品进行比较,进而发现其耐蚀性规律。结果 经过不同的热处理后,非晶合金在质量分数为3.5%的NaCl溶液中的电化学腐蚀结果相差较多。结论 在保温时间和冷却方式不变时,随着热处理温度的增加,非晶合金的耐蚀性呈下降趋势。退火温度为540 ℃时,非晶合金的耐蚀性能最佳。     

用热分析技术研究非晶态合金的退火转变动力学

论述了示差扫描热分析（ＤＳＣ）和热重分析（ＴＧ）在研究非晶态合金退火转变动力学方面的应用。利用多速率示差扫描热分析技术和热重分析技术,辅之以其它性能参量的测定和Ｘ射线衍射分析,可对反映非晶态合金退火转变动力学特征的重要参数－－－激活能进行测定,并借此分析退火转变动力学以及各个不同过程之间的联系。     

镁合金的塑性变形机制和孪生变形研究

概述了镁合金的塑性变形机制,介绍了镁合金的主要孪生系及其表征技术,详细分析了变形温度、变形速率、受力方向和晶粒尺寸等对镁合金孪生变形的影响,讨论了孪生变形对镁合金塑性变形、动态再结晶、力学性能与断裂的影响。孪生通常发生在粗大晶粒中,晶粒细化可以激活镁合金中的非基面滑移,抑制孪生变形和降低镁合金的各向异性,指出细晶镁合金的研制和工业化生产是变形镁合金发展的重要方向。     

Influence of Plastic Deformation Capacity on Failure Behavior of Pipelines

Plastic deformation capacity parameters affect the deformability of steel in the plastic stage and then affect the limit pressure of pipelines. This paper investigates the influence of plastic deformation capacity parameters on the limit bearing capacity of pipelines. These parameters include yield-to-tensile ratio (\(\sigma_{y} /\sigma_{u}\)), percentage uniform elongation (\(\delta\)) and strain hardening exponent (n). Based on the Swift strain hardening model, the relational expression of the plastic deformation capacity parameters is theoretically deduced. Ninety-five groups of material tensile test data have been collected. Based on these test data, the variation tendency of the plastic deformation capacity parameters has been analyzed statistically, and the empirical formula of the key parameters has been fitted numerically. Twenty groups of finite element examples are designed to analysis the influence of yield-to-tensile ratio and uniform elongation on the limit pressure of pipeline. Results show that, with the improvement in strength grade of steel, the plastic deformability of steel decreases; the recommended critical plastic deformation capacity indexes are: (1) pipeline steel below X65, \(\sigma_{y} /\sigma_{u}\) ≤ 0.85 and \(\delta\) ≥ 10%; (2) pipeline steel for X70–X80, \(\sigma_{y} /\sigma_{u}\) ≤ 0.93 and \(\delta\) ≥ 8%.     

镁合金在大变形和高应变率下塑性变形研究进展

介绍了强应变塑性大变形下镁合金研究现状.重点综述了在较高应变率及冲击载荷作用下关于镁合金变形的研究情况,同时也比较详细地综述了在不同温度、不同载荷作用下镁合金塑性变形特征及其物理机制.最后简要介绍了几个描述材料在较高应变率和冲击载荷作用下变形行为的数学表示式,并就镁合金作为结构材料的研究说明了作者的一些看法.     

A Model of Dynamic Recrystallization in Alloys during High Strain Plastic Deformation

1.IntroductionVerysmallrecrystallizedgrainswereobservedintheadiabaticshearbandsinmetalswhentheywereheavilydeformedathighstrainrates,whichwerezonesofhighlylocalizedplasticdeformation[1~5].Pak[1]foundthatshearbandsinacommerciallypuretitaniumwereconsistedofsmallgrainsof5o~3Oonmindiameterwithwell-definedboundaries.Chokshi[2],And.ade[3jandHinesI4Jalsoobservedtherecrystal-lizedgrainswith1oO~2Oonmdiameterswithintheshearbandsofcopper.Cho151showedthattherewereequiaxedcellswiththesizesof2oo~5oonminth…     

Influence of Moderate Temperature Treatment on Thermal Cycling Behaviour and Mechanical Properties of the CuAINiMnTi Alloys

The influence of moderate temperature treatment after quenching on thermal cycling behaviour andmechanical properties of the CuAlNiMnTi shape memory alloys have been investigated.It is shownthat there will be α phase precipitation in the alloy when it is subjected to quenching followed bymoderate temperature treatment at 600℃.The precipitation of α phase can suppress NiAl-basephase precipitation during subsequent thermal cycling,therefore the stabilization of transformationtemperature during thermal cycling can be achieved.The suitable amount of α phase precipitationcontributes to the improvement of mechanical properties of the alloy by changing the fracturemorphology.     

Thermal Stability of Fe82Nb2B14REM2 Amorphous Alloys

Materials Science - We analyze the thermal stability and kinetic parameters of crystallization of Fe82Nb2B14REM2 (REM = Y, Gd, Tb, or Dy) amorphous metallic alloys by the method of differential...