Deformation mechanism and tribological behavior of hydrogen-free carburized layer on Ti-6Al-4V alloy

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Tian Tian ◽  
Ruibo Zhao ◽  
Dongbo Wei ◽  
Kai Yang ◽  
Pingze Zhang
Keyword(s):  
Peer Review ◽  
Deformation Mechanism ◽  
Tribological Behavior ◽  
Scratch Test ◽  
Hardness Profile ◽  
Cross Sectional ◽  
Content Type ◽  
Elastic Plastic ◽  
The Coefficient Of Friction ◽  
Carburized Layer

Purpose The purpose of this paper is to expound the relationship among microstructure, mechanical property, tribological behavior and deformation mechanism of carburized layer deposited on Ti-6Al-4V alloy by double-glow plasma hydrogen-free carburizing surface technology. Design/methodology/approach Morphologies and phase compositions of the carburized layer were observed by scanning electron microscope and X-ray diffraction. The micro-hardness tests were used to evaluate the surface and cross-sectional hardness of carburized layer. The reciprocating friction and wear experiments under various load conditions were implemented to investigate the tribological behavior of carburized layer. Moreover, scratch test with ramped loading pattern was carried out to illuminate the deformation mechanism of carburized layer. Findings Compared to substrate, the hardness of surface improved to ∼1,100 HV0.1, while the hardness profile of carburized layer presented gradual decrease from ∼1,100 to ∼300 HV0.1 within the distance of the total carburizing-affected region about 30 µm. The coefficient of friction, wear rate and wear morphology of carburized layer were analyzed. Scratch test indicated that the deformation process of carburized layer could be classified into three mechanisms (elastic, changing elastic–plastic and stable elastic–plastic mechanisms), and the deformation transition of the carburizing-affected region was from changing elastic–plastic to elastic mechanisms. Both the elastic and changing elastic–plastic mechanisms are conducive to the wearing course. Originality/value Using this technology, hydrogen embrittlement was avoided and wear resistance property of titanium alloy was greatly improved. Simultaneously, the constitutive relation during the whole loading process was deduced in terms of scratch approach, and the deformation mechanism of carburized layer was discussed from a novel viewpoint. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2019-0489/

Frictional characteristics of thin-walled tubes in liquid impact forming

2019 ◽  
Vol 72 (5) ◽  
pp. 637-643
Author(s):  
Jianping Ma ◽  
Lianfa Yang ◽  
Yulin He ◽  
Jian Guo
Keyword(s):  
Stainless Steel ◽  
Peer Review ◽  
Deformation Process ◽  
Design Methodology ◽  
Steel Tubes ◽  
Content Type ◽  
Liquid Impact ◽  
The Coefficient Of Friction ◽  
Thin Walled ◽  
Short Time

Purpose This paper aims to study frictional characteristics of thin-walled tubes in the liquid impact forming (LIF) process. Design/methodology/approach LIF experiments under various impacting velocities were performed on SUS304 stainless steel tubes with various guiding lengths on a custom-designed measurement system to investigate the effects of impacting velocity and guiding length on the coefficient of friction (COF) in the guiding zone. Findings The results indicate that the COF changes dynamically in the guiding zone and decreases with the deformation process. The reduction range of the COF is wider in LIF than in both the conventional and pulsating hydroforming (THF), which may be contributed to the impacting velocities in a short time. Moreover, the COF decreases faster in the first half of the LIF process than in the second half. Under different impacting velocities and guiding lengths, the decreasing rate of the COF in the first half is more sensitive and obvious than that in the second half. Originality/value A method for determining the COF in the guiding zone in LIF is proposed and the frictional characteristics in LIF are studied. Comparing the COF of tubes in conventional THF, pulsating THF and the LIF process is valuable for improving and predicting the tubular formability in various hydraulic environments for industrial production. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0269

Metallurgical and tribological aspects for squat formation in the aluminothermic weld HAZ edges of rails welded using aluminothermy

2020 ◽  
Vol 72 (9) ◽  
pp. 1123-1131
Author(s):  
Luiz Henrique Dias Alves ◽  
Tiago Carvalho Tepedino ◽  
Mohammad Masoumi ◽  
Gustavo Tressia ◽  
Helio Goldenstein
Keyword(s):  
Weld Metal ◽  
Peer Review ◽  
Microstructural Characterization ◽  
Tensile Tests ◽  
Hardness Profile ◽  
Content Type ◽  
Heavy Haul ◽  
Pin On Disk ◽  
Tribological Characterization

Purpose The purpose of this paper is to present the results of a metallurgical, mechanical and tribological characterization of the weld and heat-affected zone (HAZ) of aluminothermic welding of premium rails used in heavy haul, looking into the origins of the squat defects associated with rail wear. Design/methodology/approach A full factorial design of experiment was carried out for 24 welds of premium and super premium rails. The factors studied were chemical composition, welding gap and preheating time. The welds were inspected visually and by ultrasound to detect superficial and internal defects and characterized by macrographic analysis, hardness profile, tensile tests and microstructural characterization in scanning electronic microscopy. Pin-on-disk test were carried out to compare the tribological behavior of the different regions of the weld rail. Findings Squat formation was shown to be associated with spheroidized pearlite regions formed on the HAZ of the welds, presenting near half the hardness of the weld metal. Thermal analysis showed that spheroidized pearlite is a result of partial austenitization at these positions. Tribological tests showed that low hardness regions presented smaller wear resistance than both the weld metal and the parent rail. Tensile test of the whole region resulted in brittle fracture along the weld metal. Originality/value The results showed that it is essential to reduce the dimensions of the HAZ and the width of the hardness drop area to mitigate squat formation in the HAZ edges. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0020/

Institutions and economic growth in ECOWAS: an investigation into the hierarchy of institution hypothesis (HIH)

2020 ◽  
Vol 47 (9) ◽  
pp. 1081-1108 ◽  
Author(s):  
Olumide Olaoye ◽  
Oluwatosin Aderajo
Keyword(s):  
Economic Growth ◽  
Panel Data ◽  
Peer Review ◽  
Cross Section ◽  
Economic Institutions ◽  
Cross Sectional ◽  
Content Type ◽  
Empirical Modelling ◽  
Data Framework ◽  
Cross Country

PurposeThe purpose of this paper is to examine the relationship between the quality of different dimensions of institutional and economic growth in a panel of 15 member ECOWAS.Design/methodology/approachThe study adopts Driscoll and Kraay′s nonparametric covariance matrix estimator, and the spatial error model to account for cross-section dependency, cross-country heterogeneity and spatial dependence inherent in empirical modelling, which has largely been ignored in previous studies. This is because, the likelihood that corruption and human capital cluster in space is very high because factors that affect these phenomena disperse across borders. Similarly, to test the threshold effect, the study adopts the more refined and more appropriate dynamic panel data which models a nonlinear asymmetric dynamics and cross-sectional heterogeneity, simultaneously, in a dynamic threshold panel data framework.FindingsThe empirical evidence supports findings by previous researchers that better-quality political and economic institutions can have positive effects on economic growth. Similarly, our results support a nonlinear relationship between political institutions and economic institution, confirming the “hierarchy of institution hypothesis” in ECOWAS. Specifically, the findings show that economic institutions will only have the desired economic outcome in ECOWAS, only when political institution is above a certain threshold.Originality/valueUnlike previous studies which assume cross-sectional and spatial independence, the authors account for cross-section dependency and cross-country heterogeneity inherent in empirical modelling.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/IJSE-10-2019-0630

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