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Competitive mechanisms occurring during quenching and partitioning of three silicon variants of 0.4 wt.% carbon steels

Publication date: March–April 2021

Source: Journal of Materials Research and Technology, Volume 11

Author(s): Ilkka Miettunen, Sumit Ghosh, Mahesh C. Somani, Sakari Pallaspuro, Jukka Kömi

Republished by Plato

Published

on

Elsevier
Volume 11, March–April 2021, Pages 1045-1060
Journal of Materials Research and Technology

open access

Abstract

Quenching and partitioning (Q&P) treated steels are traditionally alloyed with silicon (Si), but its precise role on microstructural mechanisms occurring during partitioning is not thoroughly understood. In this study, dilatometric analysis has been combined with detailed microstructural characterization to unravel the competing mechanisms occurring during partitioning either in parallel or in succession. Three 0.4 wt.% carbon steels with varying Si contents were quenched to 150 °C for ~20% untransformed austenite, and partitioned for 10–1000 s in the temperature range 200–300 °C. The steel with low Si content (0.25 wt.%) exhibited substantial bainitic transformation during partitioning at 300 °C and only 4% retained austenite (RA) at room temperature (RT) even after 1000 s hold. In contrast, a high Si fraction (1.5 wt.%) enabled retention of ~18% austenite under similar conditions. While η-carbides precipitated within the martensite laths in the high-Si steel, cementite precipitated in the low-Si variant. Furthermore, carbide precipitation and growth were strongly suppressed by high Si content. Secondary martensite formation occurred from carbon-enriched austenite during final cooling, irrespective of Si-content. Results illustrate that Si retards austenite decomposition at higher partitioning temperatures but does not improve carbon partitioning at lower temperatures.

Keywords

Quenching and partitioning

Dilatometry

Martensite

Bainite

Retained austenite

Carbides

© 2021 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785421000867?dgcid=rss_sd_all

Material

Synthesis of clay geopolymers using olive pomace fly ash as an alternative activator. Influence of the additional commercial alkaline activator used

Publication date: May–June 2021

Source: Journal of Materials Research and Technology, Volume 12

Author(s): M.A. Gómez-Casero, F.J. Moral-Moral, L. Pérez-Villarejo, P.J. Sánchez-Soto, D. Eliche-Quesada

Republished by Plato

Published

on

open access

Abstract

In this research, the use of olive pomace fly ash (OPFA) as an alkaline source for the activation of calcined clays (CC) from Bailén (Jaén, Spain) was studied. The optimal composition was obtained for 70 wt % CC and 30 wt % OPFA. The physical, mechanical and thermal properties of control geopolymers that use water as a liquid medium have been studied and compared with geopolymers that use additional activating solutions as sodium or potassium hydroxide solutions (8 M), or a mixture of alkaline hydroxide and alkaline silicate solution (NaOH–Na2SiO3 or KOH–K2SiO3). The results showed that OPFA can be used as an alkaline activator, showing mechanical properties slightly lower than those obtained when additional alkaline hydroxide activating solutions were used. The best compressive strength was obtained for geopolymers that use alkaline silicates as an activating solution. However, the best thermal insulation properties were obtained for control geopolymers. The microstructural characteristics of the geopolymers were evaluated by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM-EDS) that corroborate the formation of geopolymeric gel in all the specimens, being the amount of gel formed greater in samples using commercial potassium activating solutions. These results demonstrate the feasibility of using this type of waste, OPFA, as activating reagents in the manufacture of geopolymers or alkaline activated materials. The manufactured geopolymers can be used as compressed earth blocks for walls and partitions, since the specimens pursue mechanical properties that comply with current regulations, presenting better thermal insulation properties.

Keywords

Geopolymers

Clay

Olive pomace fly ash

Valorization

Alkaline activator

Sustainability

© 2021 The Author(s). Published by Elsevier B.V.

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Source: https://www.sciencedirect.com/science/article/pii/S223878542100329X?dgcid=rss_sd_all

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Material

Thermo-mechanical modeling and analysis of friction spot joining of Al alloy and carbon fiber-reinforced polymer

Publication date: May–June 2021

Source: Journal of Materials Research and Technology, Volume 12

Author(s): Ninshu Ma, Peihao Geng, Yunwu Ma, Katsushi Shimakawa, Jeong-Won Choi, Yasuhiro Aoki, Hidetoshi Fujii

Republished by Plato

Published

on

open access

Abstract

A three-dimensional finite element thermal-mechanical coupling model was developed to simulate the friction spot joining with a flat shoulder tool for AA6061-T6 Al alloy and carbon fiber reinforced polymer (CFRP) at different welding conditions. When joining at 1500 rpm rotation speed and 0.1 mm/s plunge speed, the peak temperature at the Al alloy-CFRP interface reached up to 575 °C as the plunge depth was increased to 0.6 mm. The interfacial temperature was reduced as rotation speed or plunge depth was decreased. Good correspondences between predicted temperature field distribution and experimental bonded area have been achieved. Thermal history and temperature distribution at the top surface of Al alloy were well validated by experimental measurements. The temperature zone within 220–340 °C made the greatest contribution to improving joint integral resistance to tensile-shear testing, which was recommended to enlarge during the process for a given welding parameter. On the basis, the design of tool structure enabling to reduce peak temperature and enlarging melted area was proved numerically as a feasible way to enlarge processing windows to increase the overall strength of joint. The findings could hopefully help optimize friction spot welded joints of dissimilar metals and composites.

Keywords

Friction spot joining

Bonding strength

CFRP/Al alloy

Numerical simulation

Heat generation

Tool design

© 2021 The Author(s). Published by Elsevier B.V.

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Source: https://www.sciencedirect.com/science/article/pii/S2238785421003380?dgcid=rss_sd_all

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Thermal and mechanical characterization of blindex glass powder residue® for the production of ecological coating

Publication date: May–June 2021

Source: Journal of Materials Research and Technology, Volume 12

Author(s): Armando C. Souza, Mayara F. Pereira, Luiz C. Mossin

Republished by Plato

Published

on

open access

Abstract

The science of materials has great interest in the development of new composites, therefore, this work aims to obtain a new material using the waste produced by the industries themselves and which in many cases produce a serious problem for the environment. For the development of this research, was used the residue in the form of mud resulting from the cutting process in the manufacture of flat glazing. The samples obtained dehydrated for 24 h at a temperature of 100 °C. The samples were pressed using hydraulic press with a capacity of 150 ton/cm2 resulting in proof body’s with dimensions in the order of 105 mm long, 52 mm wide and 5.7 mm thick and submitted the process of sintering at different temperatures in ambient atmosphere. The characterizations of proof bodies applying thermal analysis technique (TGA), presented evaporation of surface H2O and to the degradation of the molecules of Na2O, K2O and P2O5 until 100 °C. In the range between 200 °C and 600 °C the curve has a more linear attributed to the thermal degradation of the Al2O3, MgO and Fe2O3 molecules and a thermal stability above 600 °C. The x-ray diffraction analyses (XRD), with the precursor glass powder presented characteristic of a standard amorphous structure and with the powders of sintered proof body’s at different temperatures, observed the characteristic peaks of calcite (CaCo3), cristobalite (SiO2), quartz (SiO2) and low silicon oxide (SiO2) crystals. The characterizations using scanning electron microscopy technique (SEM) show a homogeneous distribution of particles with sizes in the order of 30 μm. The mechanical characterizations in the specimens applying bending rupture tests showed range of rupture modules of the 31.92 kgf/cm2 and 55.28 kgf/cm2 to the range temperature between 200 °C and 600 °C. The characterizations and water absorption tests apresented that there is a great advantage in the use of blindex® glass powder residue for the manufacture of a new ecological coating, this material can be applied more abrasively to paving blocks, septic sewer tanks, grease traps, wall building blocks and in the most finished form it can be applied as a tactile floor, internal coatings in the form of tablets for bathroom and kitchen and other finishes to the civil construction sector.

Keywords

Composite

Glass powder

Residue

Civil construction

© 2021 Published by Elsevier B.V.

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Source: https://www.sciencedirect.com/science/article/pii/S2238785421003264?dgcid=rss_sd_all

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