Effect of the crystallinity of diamond coatings on cemented carbide inserts on their cutting performance in milling

Micro-crystalline diamond (MCD) coatings were deposited on cemented carbide inserts at different temperatures using hot filament chemical vapor deposition technique. For investigating the effect of the developed diamond crystallinity on the fatigue strength and wear behaviour of the prepared MCD coated inserts, inclined impact tests and milling investigations were conducted correspondingly. Raman spectra were recorded for capturing the crystalline phases after the film deposition and their potential changes after the impact and milling experiments induced by the mechanical and thermal loads. Thus, the explanation of the cutting performance of the employed diamond coated inserts with various crystalline phases was enabled.     

Effect of high temperature annealing on ultrahard polycrystalline diamond in air and vacuum conditions

The effect of high temperature annealing on ultrahard polycrystalline diamond (UHPCD) has been investigated in air and vacuum conditions up to 1500 °C. The thermal stability, carbon bonds, morphologies and wear resistance of UHPCD were evaluated by thermal gravimetric-differential scanning calorimetry (TG-DSC), Raman spectroscopy, scanning electron microscopy (SEM) and wear tester. The thermal analysis results indicated that the thermal stability of chemical vapor deposited (CVD) diamond was better than that of polycrystalline diamond (PCD) even though it was weakened by high pressure high temperature treatment, while no graphitization was observed on UHPCD in flowing argon up to 1500 °C. When the UHPCD annealed in air, the oxidation damage with the extension of cracks and spalling holes was observed on CVD diamond as the evolution of temperature. The result confirmed by the changes of diamond peak position and full width at half maximum (FWHM) in Raman spectra curves. The PCD had shown the damage with cracks induced exfoliation of binder regions and cracks ruined diamond grains. However, the diamond peak position and FWHM of CVD diamond and PCD showed slight reduction as a function of vacuum annealing temperature with no detectable change of morphologies. The high temperature annealing has strong impact on the wear resistance of UHPCD in air while slightly in vacuum.     

Microstructure and grain growth in rapidly solidified aluminum

Grain structures in splat-quenched samples of pure aluminum and a dilute aluminum-manganese alloy have been studied, and the effect of heat treatment on grain size has been investigated. The quenched samples were examined by a novel technique allowing surface structures and grain structures to be observed simultaneously, and interesting discrepancies between these were revealed. The grain structures showed considerable resistance to grain growth on heat treatment. This has been explained and the surface and grain structures reconciled on the basis that the material self-anneals to a considerable extent immediately following solidification. The scope of this study is extended to characterize the relationship between grain structures in consolidated and extruded Al-1.3% Mn and the structure of the starting material.     

高淬透性硼微合金化特厚板钢成分优化设计

海洋工程用特厚板钢通常要求具有良好的淬透性,合理设计此类钢化学成分是改善其淬透性的主要方法之一.传统钢成分设计大多以实验为主,耗费巨大.本文以热力学计算软件Thermo-Calc和材料性能计算软件JMat Pro为工具,采用计算、预测与实验相结合的研究模式,对含B微合金化特厚板钢进行成分优化,以期获得高淬透性能.使用Thermo-Calc计算了B微合金化钢的热力学平衡析出相.通过对析出相的析出温度、析出量及相间关系分析,阐述了此类钢的成分设计原则,给出了可获得高淬透性的B微合金化钢的设计成分.采用JMat Pro对设计钢淬透性进行预测,预测结果很好地说明了设计钢成分的合理性.经过淬透性实验和化学相分析,进一步肯定了优化设计结果.理论计算与实验结果表明高铝含量有利于改善硼微合金化钢淬透性.     

低碳钢中纳米尺寸碳化物的相间析出行为

采用扫描电镜和透射电子显微镜对低碳Ti-Mo系的热轧板进行了组织分析,同时对其中的纳米粒子析出行为进行了研究.强化机理分析表明析出强化对于屈服强度的贡献值可达291 MPa.随着卷取温度的降低,纳米粒子相间析出的排间距会减小,相间析出的排间距与其在铁素体中形核点位置有一定的离散值,但基本上呈一定的固定值.α/γ界面的观察和采用不同理论的计算结果表明相间析出的产生主要与α/γ界面的台阶形成有关,相间析出的排间距大小由台阶高度、晶界扩散系数、等温温度、台阶面迁移速率等决定.     

Considerations sur la seluence de precipitation dans les alliages aluminium-linc

le have studied the ageing of aluminium-linc alloys by X-ray scattering and electron microscopy over the temperature range t-80°C to + 150°C. Only tlo precipitated phases have been observed:

• 1.(1) Guinier-Preston lones for lhich the sile effect has a constant value of ϵt- t-0.018. le have also calculated the crystalline lattice deformation inside the lones. These deformations are of the rhombohedral type such that the lones become ellipsoidal and for the greatest sile of lones are of the same order of magnitude as these characterising the phase χt'_R.
• 2.(2) A semi-coherent hexagonal precipitate the parameters of lhich are found to be close to these pure linc.

     

Solute segregation and precipitation under heavy-ion bombardment

Solute segregation and precipitation in dilute Ni-base binary alloys during heavy-ion bombardment were studied using a kinetic model. Spatially-dependent defect—production rates corresponding to 75-keV and 3-MeV Ni⁺ ion bombardment and various defect—solute interactions were considered in the calculations. For strong interstitial—solute binding, solutes in the peak-damage region are transported to the sample surface and into the bulk beyond the damage range, resulting in a solute depletion at the damage peak. However, for a vacancy—solute binding energy of ~0.05 eV, the solute-segregation trends are reversed from the strong interstitial—solute interaction case. With larger vacancy—solute binding energies, solute enrichment occurs at the surface. The present theoretical predictions are qualitatively compared with recent experimental measurements of the temperature and spatial dependence of radiation-induced segregation of undersize and oversize solutes in Ni-base alloys.