Electron Beam Surface Treatment. Part I: Surface Hardening of AISI D3 Tool Steel

The effects of electron beam surface hardening treatment on the microstructure and hardness of AISI D3 tool steel have been investigated in this paper. The results showed that the microstructure of the hardened layer consisted of martensite, a dispersion

Electron Beam Surface Remelting of AISI D2 Cold-Worked Die Steel

Electron beam surface remelting has been carried out on AISI D2 cold-worked die steel. The microstructure and hardening behavior of the electron beam surface remelted AISI D2 cold-worked die steel have been studied by means of optical microscopy and Vickers hardness testing. It was found that AISI D2 steel can be successfully surface hardened by electron beam surface remelting. This surface hardening effect can be attributed to microstructural refinement following electron beam surface remelting. (C) 2002 Elsevier Science B.V. All rights reserved.

尼龙1010的蠕变性质

本文给出了尼龙1010材料在不同温度和不同应力水平下的实验结果,提出了包含蠕变激活能的蠕变方程,该方程与实验数据良好符合。文中用时温等效方法处理了蠕变与松弛的数据,寻求了它们之间的一致性。

Mixed-mode fracture mechanisms near the fatigue threshold of aisi-316 stainless-steel

Near threshold, mixed mode (I and II), fatigue crack growth occurs mainly by two mechanisms, coplanar (or shear) mode and branch (or tensile) mode. For a constant ratio of ΔK_I/ΔK_II the shear mode growth shows a self-arrest character and it would only start again when ΔK_I and ΔK_II are increased. Both shear crack growth and the early stages of tensile crack growth, are of a crystallographic nature; the fatigue crack proceeds along slip planes or grain boundaries. The appearance of the fracture surfaces suggest that the mechanism of crack extension is by developing slip band microcracks which join up to form a macrocrack. This process is thought to be assisted by the nature of the plastic deformation within the reversed plastic zone where high back stresses are set up by dislocation pile-ups against grain boundaries. The interaction of the crack tip stress field with that of the dislocation pile-ups leads to the formation of slip band microcracks and subsequent crack extension. The change from shear mode to tensile mode growth probably occurs when the maximum tensile stress and the microcrack density in the maximum tensile plane direction attain critical values.

尼龙1010的平衡热力学参数及其γ-辐照产物的结晶过程

尼龙1010是我国特有的工程塑料。但对它的结构与性能的基础研究并不多见。迄今为止，许多聚酰胺的晶胞参数已被测定，并比较准确地计算出它们的结晶密度ρ_c。可是，尚未见到过有关尼龙1010的ρ_c的报道。此外，结晶高聚物的平衡熔融温度T°_m和平衡熔融热ΔH°_m是非常重要的热力学参数，尤其是后者更是用量热法计算结晶度的基准。早在50年代，Flory等对它的T°_m和ΔH°_m进行了许多研究，由于受当时历史条件限制，这些数值的准确性不高，不能当作平衡状态的数值。尼龙1010经γ-射线辐照后，有可能提高它的使用温度，扩大它的应用范围和领域。但至今未见到过大剂量下γ-辐照尼龙1010及其添加强化交联剂BMI的γ辐照产物的热学性能和结晶过程的研究。随着科学技术的发展，目前迫切需要准确的尼龙1010的ρ_c、T°_m、ΔH°_m的数值，以及大剂量下γ-辐照产物的热学性能和结晶过程的详细研究，以便更合理地开发和利用这一材料为四化建设服务。本文用DSC差示扫描量热仪、红外光谱仪、广角X-射线衍射仪以及TMS热机械仪等研究手段，准确地测定了尼龙1010的平衡热力学参数，并对尼龙1010及其添加强化交联剂BMI的γ-辐照产物的热学性能和结晶过程进行了详细的研究。用红外吸光度-密度外推法求得尼龙1010的ρ_a（非晶密度）= 1.003 ρ_c = 1.098g/cm~3。1.098g/cm~3与用X-射线衍射法求得的1.135g/cm~3比较，认为后者更为合理。用介稳态结晶试样的ΔH_m-(V-bar)_(sp)的线性关系，求得尼龙1010的平衡熔融热。ΔH°_m = 244.0J/g。企图用常用的Hoffman Tm-Tc外推法来确定尼龙1010的平衡熔融温度T°_m，但未能成功，并指出其升温过程中重结晶异常迅速是此法行不通的主要原因。用Kamide提出的双重外推法成功地求得尼龙1010的平衡熔融温度：T°_m = 487 K = 214 ℃通过详细地研究尼龙1010及其添加强化并联剂BMI的γ辐照产物的热学性能，发现强化交联剂BMI的加入，使尼龙1010大分子的交联更容易，但也使得空间网络较松散；同时γ辐照尼龙1010在再次等速升温过程中出现冷结晶峰是辐照产物中存在可结晶部分、交联网络阻碍可结晶部分结晶两者共同作用的结果。交联网络使可结晶部分在降温过程中来不及结晶，当再次升温到玻璃化转变温度以上时，链段冻结被解除，可结晶的分子链段进行有序排列而结晶，导致冷结晶峰的出现。冷结晶峰的强度和位置与辐照产物中可结晶部分的多少、交联网络的大小即相邻交联点之间的分子量Mc的大小、交联网络的松散程度以及试样的热历史都有关。选择适当的等温结晶温度，用DSC-2C型差示扫描量热仪研究了尼龙1010及其γ-辐照产物和添加强化交联剂BMI的γ-辐照产物的等温结晶过程。用DSC-2C 3600 TADS计算机自带的部分面积程序进行动力学数据处理。通过仔细的等温结晶动力学研究，发现γ辐照尼龙10104 Avrami指数n几乎不受辐照剂量R和强化交联剂BMI的影响，且一般为3.75，这说明尼龙1010及其γ辐照产物的结晶过程接近于均相三维成核。随着辐照剂量R和强化交联剂BMI含量的增大，折迭链表面自由能σe值增大，σe值的分布可能变宽，σe值的这种变化可以归因于辐照剂量R和强化交联剂BMI的含量增大时，交联网络增多，交联密度增大，Mc值的分布变宽，链尾和小链圈的数目增多，活动性减小，同时链尾也增长，结果导致σe（链尾、链圈）增大，从而σe值变大，σe值的分布可能变宽。σe值的这种变化也正是过冷度增大、拖尾现象严重、总的动力学速率常数Kn和结晶速率t_(0.5)~(-1)变小的总根源。由此可见，对于分子量不同或分子结构有差别的同一种结晶高聚物来说，σe值可以作为衡量结晶能力大小的定量标准。

Crystallization behavior of carbon nanotubes-filled polyamide 1010

The nanocomposites of polyamide1010 (PA1010) filled with carbon nanotubes (CNTs) were prepared by melt mixing techniques. The isothermal melt-crystallization kinetics and nonisothermal crystallization behavior of CNTs/PA1010 nanocomposites were investigated by differential scanning calorimetry. The peak temperature, melting point, half-time of crystallization, enthalpy of crystallization, etc. were measured. Two stages of crystallization are observed, including primary crystallization and secondary crystallization. The isothermal crystallization was also described according to Avrami's approach. It has been shown that the addition of CNTs causes a remarkable increase in the overall crystallization rate of PA1010 and affects the mechanism of nucleation and growth of PA1010 crystals. The analysis of kinetic data according to nucleation theories shows that the increment in crystallization rate of CNTs/PA1010 composites results from the decrease in lateral surface free energy.

Annealing of nylon-1010 under high pressure

Full Paper: A study has been made on the annealing of nylon-1010 under high pressures. Heat treatment of melt-crystallized nylon-1010 was performed at 250degreesC for 30 min in the pressure range 0.7 similar to 2.5 GPa. It was found that the triclinic crystals of virgin nylon-1010 were retained at pressures less than 1.0 GPa or larger than 1.2 GPa. The X-ray diffraction intensity of (100) planes decreased with increasing pressure. The diffraction peaks shifted slightly to higher angles (2theta) relative to the virgin nylon-1010, indicating dense packing of polymer chains at high pressures. The highest melting temperature was 208degreesC for the sample annealed at 1.5 GPa. No extended-chain crystals were formed under the experimental conditions. Crosslinking occurred in the pressure range 1.0 similar to 1.2 GPa. The structure of the crosslinked samples was characterized by means of infrared spectroscopy and X-ray photoelectron spectroscopy. It is concluded that a mechanism of crosslinking via carbodiimide can explain the nature of crosslinking of nylon-1010 annealed at high pressures. The remarkable changes of the structure of annealed nylon-1010 are also discussed in this article.

Compatibilization of side-chain, thermotropic, liquid-crystalline ionomers to blends of polyamide-1010 and polypropylene

A novel side-chain, liquid-crystalline ionomer (SLCI) with a poly(methyl hydrosiloxane) main chain and side chains containing sulfonic acid groups was used in blends of polyamide-1010 (PA1010) and polypropylene (PP) as a compatibilizer. The morphological structure, thermal behavior, and liquid-crystalline properties of the blends were investigated by Fourier transform infrared, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy. The morphological structure of the interface of the blends containing SLCI was improved with respect to the blend without SLCI. The compatibilization effect of greater than 8 wt % SLCI for the two phases, PA1010 and PP, was better than the effects of other SLCI contents in the blends.

Crystallization and Crosslinking of polyamide-1010 under elevated pressure

The structure and thermal properties of polyamide-1010 (PA1010), treated at 250degreesC for 30 min under pressures of 0.7-2.5 GPa, were studied with wide-angle X-ray diffraction (WAXD), infrared (IR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Crystals were formed when the pressures were less than 1.0 GPa or greater than 1.2 GPa. With increasing pressure, the intensity of the diffraction peak at approximately 24degrees was enhanced, whereas the peak at approximately 20degrees was depressed. The triclinic crystal structure of PA1010 was preserved. The highest melting temperature of the crystals obtained in this work was 208degreesC for PA1010 treated at 1.5 GPa. Crosslinking occurred under pressures of 1.0-1.2 GPa. Only a broad diffraction peak centered at approximately 20degrees was observed on WAXD patterns, and no melting and crystallization peaks were found on DSC curves. IR spectra of crosslinked PA1010 showed a remarkable absorption band at 1370 cm(-1). The N-H stretching vibration band at 3305 cm(-1) was weakened. Crystallized PA1010 had a higher thermal stability than crosslinked PA1010, as indicated on TGA curves by a higher onset temperature of decomposition.

压力对尼龙1010凝聚态结构的影响

研究了尼龙(PA)1010在250℃、不同压力下退火30 min后凝聚态结构的变化。结果表明,在压力小于1.0 GPa和大于1.2 GPa的范围内,PA1010室温结晶的三斜晶系的晶体结构没有变化,但是(100)晶面的衍射强度随压力的增加而减弱,而(110/010)晶面的衍射强度增加;当压力在1.0～1.2 GPa时,PA1010的X射线衍射图谱没有明显的衍射峰,DSC和溶解实验证实,PA1010在该压力范围内发生了交联,并进一步讨论了PA1010在高压下发生交联的机理。