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Material

Microstructure and mechanical properties of 34CrNiMo6 steel repaired by laser remelting

Publication date: November–December 2020

Source: Journal of Materials Research and Technology, Volume 9, Issue 6

Author(s): Renyu Liang, Chunping Huang, Hongwei Hao, Fenggang Liu, Fencheng Liu, Menghua Song, Liming Ke

Republished by Plato

Published

on

open access

Abstract

Laser remelting can be used not only to improve the metal surface structure, but also to repair metal surface defects. 34CrNiMo6 belongs to European standard high strength alloy structural steel. It has been widely used in the manufacture of large-size shaft parts which are prone to defects such as cracks and wear during service. This study proposed a repair method for these defects by laser remelting the filled block and then performed heat treatment. The microstructure, m9icrohardness and tensile strength of the repaired sample and heat-treated sample were analyzed using scanning electron microscope (SEM), Vickers hardness tester and universal tensile tester. The final results showed that the metallurgical bonding between the substrate and the filler was good. The microstructure of repaired sample could be divided into three regions: I, II, and III. The main microstructure in region I and II was tempered martensite, and in region III was bainite and martensite. Different regions of repaired sample presented uneven hardness distribution, and the fracture mode was quasi-cleavage fracture. However, after heat treatment, the microstructure of the sample was tempered martensite. Its hardness became uniform, and the fracture mode of the heat-treated sample was ductile fracture. The average hardness value of the heat-treated sample was 296.4HV0.2, which was slightly higher than the substrate. The tensile strength value of the heat-treated sample reached 972.91MPa, which was about 99.3 % of substrate, and its elongation δ was 14.25 %. Overall, the mechanical properties were close to those of the forging.

Keywords

Laser remelting repair

34CrNiMo6 steel

Microstructure

Mechanical properties

© 2020 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420318251?dgcid=rss_sd_all

Material

Electron microscopy study of laser welded GH909 superalloy joint

Publication date: November–December 2020

Source: Journal of Materials Research and Technology, Volume 9, Issue 6

Author(s): Zhengwu Zhu, Xiuquan Ma, Gaoyang Mi, Chunming Wang

Republished by Plato

Published

on

open access

Abstract

The formation process of gamma/Laves eutectic constituents were systematically investigated in both heat-affected zone (HAZ) and fusion zone (FZ) of laser-welded GH909 superalloy. Solidification sequences and eutectic reactions were proposed by morphologically and chemically analyzing phase and chemical composition by utilizing various characterization methods. In FZ, the ultimate eutectic constituents experienced three stages: 1) liquid (L)→Primary gamma (γ) (1360 °C), forming a γ dendritic morphology; 2) following L→γ+(Nb, Ti)C precipitation at mushy zone; 3) terminal L→γ+Laves (1184 °C) at γ interdendritic regions. Enrichment of Nb in Laves and surrounding γ produced a high dislocation density in eutectic constituents. Continuous distribution of such γ/Laves structures promoted the formation of micro interdendritic solidification cracks under accumulated tensile stress. In HAZ, however, the fraction of γ/Laves constituents was heat input depended and increased as the reduction of distance from fusion line. An interactionally and simultaneously integrated process NbC+γ→Laves (~1323 °C) caused the formation of eutectic constituents with NbC decomposition, Laves formation, grain boundary liquation and subsequently eutectic reactions.

Keywords

GH909 superalloy

Laser welding

Solidification sequence

Eutectic constituents

© 2020 Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420319074?dgcid=rss_sd_all

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Material

Two pass laser welding of 304 stainless to TC4 Titanium alloy using Monel 400/Nb bilayer

Publication date: Available online 26 November 2020

Source: Journal of Materials Research and Technology

Author(s): YuanBo Bi, Yan Zhang, Kai Liu, Yan Xu, Jian Ping Zhou

Republished by Plato

Published

on

Elsevier

Available online 26 November 2020

Journal of Materials Research and Technology

open access

Abstract

Laser welding was performed to join 304 stainless steel (SS) and TC4 Titanium (Ti) alloy using Monel 400/Nb bilayer. In order to avoid the formation of Ti-based and Nb-Fe intermetallics, a hybrid joint based on two welding mechanisms was created. Two pass welding involves creating two fusion weld separated by unmelted Monel 400 and Nb interlayer. The first laser pass was focused on the 304 SS side, a weld zone of the mixing of molten Monel400 and 304 SS was formed. The second laser pass was focused on the TC4 Ti alloy side, a weld zone of the mixing of molten Nb interlayer and TC4 Ti alloy was formed. The joining between the Monel 400 and Nb interlayer was achieved by atoms interdiffusion. The joint fractured at the Monel 400-Nb interface with maximum tensile strength of 258 MPa.

Keywords

welding

304 stainless steel

TC4 Ti alloy

bilayer

interface

tensile strength

© 2020 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320263?dgcid=rss_sd_all

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Material

Colorful and antibacterial nylon fabric via in-situ biosynthesis of chitosan mediated nanosilver

Publication date: Available online 26 November 2020

Source: Journal of Materials Research and Technology

Author(s): K. M. Faridul Hasan, Haona Wang, Sakil Mahmud, Md Anwar Jahid, Moyinul Islam, Wangbao Jin, Cao Genyang

Republished by Plato

Published

on


Elsevier

Available online 26 November 2020

Journal of Materials Research and Technology

open access

Highlights

Chitosan mediated AgNPs were in-situ synthesized on nylon fabric via an eco-friendly approach.

The synthesized AgNPs can serve as a colorant (red, yellow, and blue) for textile coloration.

Traditional cytotoxicity of silver was systematically staved off by control synthesis.

Producing a durable and highly efficient antibacterial property on nylon fabric.

Abstract.

Abstract

Herein, functionalization of nylon fabric surfaces in terms of excellent coloration and antibacterial properties were developed by in-situ synthesis of chitosan mediated silver nanoparticles (AgNPs). No toxic chemicals were used to ensure eco-friendly conditions. The variation of colors (nearly red, yellow, and blue) was achieved by only regulating precursor concentration and utilization of ascorbic acid. Functionalized nylon fabrics were then characterized by investigating surface morphology, elemental mapping, metal composition, and chemical linkage among compositing components. Results exposed that the particles are within the nano-range size, spherical in shapes, homogenously dispersed over the surfaces, and firmly attached to the nylon fiber by molecular force or double networking properties of chitosan. Color characteristics demonstrate a uniform shade due to the localized surface plasmon resonance (LSPR) properties of AgNPs with brilliant colorfastness and color strength (K/S). The antibacterial properties are found to be significant, with more than 88% bacterial reduction rate against both the gram-positive and gram-negative bacteria even after 20 washing cycles. Overall, this nylon functionalization protocol without using traditional chemicals like crosslinkers, binders, or coating agents provides the desired permanent efficiency and safe product.

Keywords

Silver nanoparticles

nylon functionalization

chitosan

primary coloration

antimicrobial

© 2020 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320226?dgcid=rss_sd_all

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