Microstructures and Properties of Extruded Al-0.6Mg-0.6Si Aluminium Alloy for High-speed Vehicle

AbstractThe Al-0.6Mg-0.6Si aluminium alloy was extruded for high-speed vehicle. The microstructure and mechanical property of extruded Al-0.6Mg-0.6Si aluminium alloy were investigated. The results of experimentation show that the tensile strength of extruded Al-0.6Mg-0.6Si aluminum alloy is above of 245MPa, and the percentage elongation after fracture is better than 8%. The microstructure is rolling structure, and the coarse second phases distribute in α-Al solid solution matrix structure. The second phases are inclusions, coarse stable phases of β′ (Mg2Si) or their collection. The tiny β′ (Mg2Si) strengthening precipitation phases mostly distribute in the grain boundary. The size of β′ strengthening phase is about 5nm. The width of no precipitation band is above of 50nm. The fatigue life is 1.061×105 cycle when σmax=0.75σb. The fatigue cracks initiate in surface of extruded Al-0.6Mg-0.6Si aluminium alloy sample. The fatigue fracture is composed of the initiation zone, the propagation zone, and the sudden fracture zone, which is characteristic of a mixed-type fatigue fracture

Использование неплавящегося вольфрамового электрода в среде аргона для поверхностного упрочнения конструкционных сталей

Лебедев, Ю. М. Использование неплавящегося вольфрамового электрода в среде аргона для поверхностного упрочнения конструкционных сталей / Ю. М. Лебедев, Yu Zhishui, В. А. Мартыненко // Зб. наук. пр. НУК. – Миколаїв: НУК, 2007. – № 4 (415). – С. 58-64.Выполнены исследования структурных превращений и геометрических характеристик зоны упрочнения при поверхностной обработке неплавящимся вольфрамовым электродом в среде аргона. Рассмотрено влияние длины дуги на геометрические характеристики зоны упрочнения

Microstructures Evolution and Micromechanics Features of Ni-Cr-Si Coatings Deposited on Copper by Laser Cladding

Three Ni-Cr-Si coatings were synthesized on the surface of copper by laser cladding. The microstructures of the coatings were characterized by optical microscopy (OM), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS). According to the analysis results of phase compositions, Gibbs free energy change and microstructures, the phases of three coatings appeared were Cr3Si+γ-Ni+Cuss (Coating 1, Ni-26Cr-29Si), Cr6Ni16Si7+Ni2Si+Cuss (Coating 2, Ni-10Cr-30Si) and Cr3Ni5Si2+Cr2Ni3+Cuss (Coating 3, Ni-29Cr-16Si). The crystal growth in the solidification process was analyzed with a modified model, which is a combination of Kurz-Giovanola-Trivedi (KGT) and Lipton-Kurz-Trivedi (LKT) models. The dendrite tip undercooling in Coating 2 was higher than those of Coating 1 and Coating 3. Well-developed dendrites were found in Coating 2. A modification of Hunt’s model was adopted to describe the morphological differences in the three coatings. The results show that Coating 1 was in the equiaxed dendrite region, while Coatings 2 and 3 were in the columnar dendrite region. The average friction coefficients of the three coatings were 0.45, 0.5 and 0.4, respectively. Obvious plastic deformation could be found in the subsurface zone of Coatings 2 and 3

Microstructure Evolution of TiC Particles In Situ, Synthesized by Laser Cladding

In this paper, a TiC reinforcement metal matrix composite coating is produced using nickel and graphite mixing powder on the surface ofTi-6Al-4V alloy by laser radiation. The microstructure of the coatings is investigated by XRD, SEM and EDS. Results show that most of the TiC phase is granular, with a size of several micrometers, and a few of the TiC phases are petals or flakes. At the cross-section of the coatings, a few special TiC patterns are found and these TiC patterns do not always occur at the observed cross-section. The even distribution of the TiC phase in the coatings confirms that the convection of the laser-melted pool leads to the homogenization of titanium atoms from the molten substrate, and carbon atoms from the preplace powder layer, by the mass transfer. The characteristics of the TiC pattern confirm that the morphology and distribution of the primary TiC phase could be influenced by convection. Two main reasons for this are that the density of the TiC phase is lower than the liquid melt, and that the primary TiC phase precipitates from the pool with a high convection speed at high temperature

Standardized Weibull statistics of ceramic strength

In order to estimate Weibull parameters in the Weibull statistical fracture theory as truly material properties independent of specimen geometry and loading mode, first the Weibull statistical fracture theory is transformed into the ordinary Weibull distribution function under certain approximation. Then the standardized format of ordinary Weibull distribution is introduced to enable Weibull modulus as the single parameter for estimation via the maximum likelihood method. The method of using standardized Weibull distribution for strength data synchronization and Weibull modulus estimation is validated by analyzing extensive strength data sets measured from uniaxial flexure, biaxial flexure and their combination, and from smooth and notched specimens. The technical path to estimate the scale parameter and threshold strength as material properties in the Weibull statistical fracture theory and effect of sample size on the estimation accuracy are also discussed

Statistical size scaling of compressive strength of quasi-brittle materials incorporating specimen length-to-diameter ratio effect

Statistical size scaling of compressive strength of quasi-brittle materials demands to define a global stress parameter pertinent to the well accepted mechanism of shear stress induced fracture. The work proposes to adopt the resultant stress acting on the diagonal cross-section of a uniaxial compression specimen from one loading end to the other loading end in place of the conventional nominal compressive stress on two loading ends for statistical size scaling. As a result, the size effect on compressive strength is partitioned into specimen volume effect and specimen length-to-diameter ratio effect according to a recently developed formulation for the generalized weakest link statistics. This proposal is validated by three published data sets on the compressive strength of concrete, rock and four cohesive soils as preliminary case studies

Statistics of ceramic strength: Use ordinary Weibull distribution function or Weibull statistical fracture theory?

"Weibull statistics" for strength distribution analysis refers to either the ordinary Weibull distribution function or the Weibull statistical fracture theory. The ordinary Weibull distribution function is an empirical distribution function on an equal footing with other type of classical empirical distributions such as normal and log-normal distributions for fitting the statistical data of various random variables nonexclusive to materials strength. It has no explicit physical meaning and cannot be used for size scaling and prediction of strength. The Weibull statistical fracture theory is a weakest-link statistical fracture model for a solid with the strength distribution of an elemental volume being described by the ordinary Weibull distribution function. It has the capability of size scaling and prediction of strength for specimens with different geometries and different loading modes. The three-parameter Weibull statistical fracture theory in uniaxial flexure of prismatic beams is reformulated and validated by both numerical and real strength experiments of different ceramics

A Statistical Model of Cleavage Fracture Toughness of Ferritic Steel DIN 22NiMoCr37 at Different Temperatures

It is a conventional practice to adopt Weibull statistics with a modulus of 4 for characterizing the statistical distribution of cleavage fracture toughness of ferritic steels, albeit based on a rather weak physical justification. In this study, a statistical model for cleavage fracture toughness of ferritic steels is proposed according to a new local approach model. The model suggests that there exists a unique correlation of the cumulative failure probability, fracture toughness and yield strength. This correlation is validated by the Euro fracture toughness dataset for 1CT specimens at four different temperatures, which deviates from the Weibull statistical model with a modulus of four

Improving the wear resistance of HVOF sprayed WC-Co coatings by adding submicron-sized WC particles at the splats' interfaces

In this paper, the submicron-sized WC particles (similar to 300 nm) with the content of 3 wt% and 5 wt.% are incorporated into high velocity oxy-fuel (HVOF) sprayed WC-Co coatings with the aim of improving properties of the coatings. XRD analyses suggest a small amount of decarburization of the incorporated WC phase after the composite coating deposition. The SEM microstructure showed even distribution of WC particles at the interfaces of WC-Co splats, indicating significantly enhanced wear resistance of the coatings with the wear rate as much as similar to 10(-7) mm(3)/N. m. The content of submicron-sized WC particles plays an important role in determining the wear performances of the coatings. The increment of submicron-sized WC particles causes a decrease in wear rate from 6.09 x 10(-7) mm(3)/N.m to 5.15 x 10(-7) mm(3)/N.m. Also, the Vickers microhardness of the coatings enhances as the increasing of WC particle ratio (reaches 1365 HV with the content of the WC particles of 5 wt.%). The wear failure analysis gives further insight into the mechanism of the property enhancement. The change of stress state and crack initiation at splats' interfaces act as the predominant mechanism, which is caused by the presence of submicron-sized WC particles at splats' interfaces. (C) 2015 Elsevier B.V. All rights reserved

Statistical size scaling of breakage strength of irregularly-shaped particles

The microdefects in a material responsible for fracture initiation in particle breakage may not always have a uniform spatial distribution. This work applies the power-law spatial flaw distribution based weakest link formulation of cumulative failure probability for statistical size scaling of breakage strength of irregularly-shaped particles. Four sets of published breakage strength data of different sized grains made of different materials including rock, basalt, sugar, and potash are adopted to validate the power-law spatial flaw distribution based weakest link model. Since the power-law spatial flaw distribution based weakest link model encompasses the uniform spatial flaw distribution based weakest link model as its subordinate member, while the Weibull statistical strength theory is a special case of the uniform spatial flaw distribution based weakest link model, this work extends the capability to investigate size scaling of particle breakage strength