Characteristics of microstructure and stresses and their effects on interfacial fracture behavior for laser-deposited maraging steel

Publication date: 5 January 2018
Source:Materials & Design, Volume 137
Author(s): Shaopeng Wei, Gang Wang, Liping Wang, Yiming Rong
Laser cladding is one of the most attractive ways to repair or remanufacture high-added-value engineering components. The present paper describes the effect of microstructure and residual stresses on the interfacial fracture behavior of laser-deposited maraging steel. The multi-layer overlapped cladding material was deposited on maraging steel substrates using laser hot-wire deposition. Residual stress profile was measured by X-ray diffraction. Temperature evolution and the induced phase transformation during the process were investigated to reveal the generation mechanism of residual stresses. A novel testing method was developed to analyze the interfacial fracture behavior and evaluate the bonding strength with specially designed T-shaped samples. The compressive stresses derived from martensitic expansion was presented in the clad layer, and tensile stresses in the heat affected zone up to a depth of 4mm, which was caused by thermal shrinkage. Both the solidification micro-voids and steep stress gradient appearing in the interface contributed to the propagation of interfacial crack that will critically affect the mechanical properties of laser deposited material.

Graphical abstract

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Phase evolution and carbon redistribution during continuous tempering of martensite studied with high resolution techniques

Publication date: 15 December 2017
Source:Materials & Design, Volume 136
Author(s): Annika Vieweg, Erwin Povoden-Karadeniz, Gerald Ressel, Petri Prevedel, Tomasz Wojcik, Francisca Mendez-Martin, Andreas Stark, Jozef Keckes, Ernst Kozeschnik
Using high resolution techniques, such as, 3D atom probe tomography, transmission electron microscopy and synchrotron radiation, the continuous tempering process of a 50CrMo4 steel is analyzed. Differences of continuous heating compared to isothermal holding at certain tempering temperatures are discussed. Focus is laid on in-depth characterization of phase development and carbon redistribution effects, such as, segregation and clustering. The results of this work suggest that segregation is the dominant effect at low temperatures (<150°C), while cluster formation within these segregated areas is prominent at intermediate temperatures (150–250°C). Epsilon carbide is formed during continuous heating with off-stoichiometric chemical composition (270–350°C). It transforms finally into cementite (T>350°C).

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An overview of elastic polymeric shape memory materials for comfort fitting

Publication date: 15 December 2017
Source:Materials & Design, Volume 136
Author(s): L. Sun, W.M. Huang, T.X. Wang, H.M. Chen, C. Renata, L.W. He, P. Lv, C.C. Wang
In this paper, we briefly review the recent progress in comfort fitting using elastic polymeric shape memory materials (SMMs). First, the required features on elastic SMMs for comfort fitting are discussed. A few types of polymeric SMMs (including some commercially available ones), which have these features, are presented. A number of prototypes made of these SMMs are used to demonstrate the feasibility to achieve the concept of comfort fitting in a one-for-all manner, i.e., one sized product to comfort fit any individuals.

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Poly(3,4-ethylenedioxythiophene) doped with various carbon-based materials as counter electrodes for dye sensitized solar cells

Publication date: 15 December 2017
Source:Materials & Design, Volume 136
Author(s): Muhammad Norhaffis Mustafa, Suhaidi Shafie, Zulkarnain Zainal, Yusran Sulaiman
Various carbon-based materials, poly(3,4-ethylenedioxythiophene) (PEDOT) and titanium dioxide (TiO2) were used to fabricate new counter electrodes namely poly(3,4-ethylenedioxythiophene)-reduced graphene oxide/titanium dioxide (PEDOT-rGO/TiO2), poly(3,4-ethylenedioxythiophene)-nanocrystalline cellulose/titanium dioxide (PEDOT-NCC/TiO2) and poly(3,4-ethylenedioxythiophene)-multiwalled carbon nanotubes/titanium dioxide (PEDOT-MWCNT/TiO2). MWCNT and rGO provided high electrical conductivity and a large surface area, whereas NCC offered a large surface area and high optical transparency which is an important criterion to fabricate a good counter electrode for enhanced dye-sensitized solar cell (DSSC) performance. In addition, carbon-based materials have high availability and low cost compared to platinum-based materials which are more expensive and difficult to source. The PEDOT-NCC/TiO2 counter electrode exhibited good electrocatalytic activity towards tri-iodide ion reduction and yielded a power conversion efficiency of 2.10%, which was much higher compared to PEDOT-rGO/TiO2 (1.11%) and PEDOT-MWCNT/TiO2 (1.29%). PEDOT-NCC/TiO2 also displayed lower charge transfer resistance (Rct1=10.4Ω·cm²) and higher cathodic peak current density (Icp=−2.60mA·cm⁻²) as compared to the other counter electrodes.

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Braided textile composites for sports protection: Energy absorption and delamination in impact modelling

Publication date: 15 December 2017
Source:Materials & Design, Volume 136
Author(s): Chen Wang, Anish Roy, Zhong Chen, Vadim V. Silberschmidt
Composites reinforced with braided textiles exhibit high structural stability and excellent damage tolerance, making them ideal materials for use in sports-protection equipment. In sports impact scenarios, braided composites need to maintain their structure integrity and dissipate impact energy to protect a human body. Thus, it is crucial to study the dynamic response of a composite structure and its energy-dissipation mechanisms. Here, a multi-scale computational approach was explored to capture main damage modes of a braided textile composite; simulations were supported by experimental verification. A drop-weight test was performed with a spike-shape impactor to imitate real-life sports impact collision scenarios, followed by X-ray computed micro-tomography to characterize damage morphology of the specimen. The experimental results were compared with analytical models. The extent of delamination was quantified by applying surface- and element-based cohesive zone models. A ply-level model with three-dimensional continuum and shell elements was employed to explore the effect of through-thickness failure modes on energy absorption of the composite. The propagation mechanism of matrix cracks is also discussed. In addition, with the developed model, impact-attenuation performance of a shin-guard structure was simulated. The presented modelling capability can improve design of braided composite structures for sports and other protective and structural applications.

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Editorial Board

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Microphthalmia with linear skin defects (MLS) syndrome: familial presentation

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