Editorial

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2 pages, 143 KiB

Open AccessEditorial

Fracture Behavior of Innovative Materials under Different Environmental Conditions

by Filippo Berto

Metals 2018, 8(5), 291; https://doi.org/10.3390/met8050291 - 24 Apr 2018

Cited by 1 | Viewed by 2367

Abstract

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(This article belongs to the Special Issue Fracture Behaviour of Innovative Materials under Different Enviromental Conditions)

Research

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18 pages, 9738 KiB

Open AccessArticle

Assessment of Ductile, Brittle, and Fatigue Fractures of Metals Using Optical Coherence Tomography

by Gheorghe Hutiu, Virgil-Florin Duma, Dorin Demian, Adrian Bradu and Adrian Gh. Podoleanu

Metals 2018, 8(2), 117; https://doi.org/10.3390/met8020117 - 08 Feb 2018

Cited by 31 | Viewed by 7035

Abstract

Some forensic in situ investigations, such as those needed in transportation (for aviation, maritime, road, or rail accidents) or for parts working under harsh conditions (e.g., pipes or turbines) would benefit from a method/technique that distinguishes ductile from brittle fractures of metals—as material [...] Read more.

Some forensic in situ investigations, such as those needed in transportation (for aviation, maritime, road, or rail accidents) or for parts working under harsh conditions (e.g., pipes or turbines) would benefit from a method/technique that distinguishes ductile from brittle fractures of metals—as material defects are one of the potential causes of incidents. Nowadays, the gold standard in material studies is represented by scanning electron microscopy (SEM). However, SEM instruments are large, expensive, time-consuming, and lab-based; hence, in situ measurements are impossible. To tackle these issues, we propose as an alternative, lower-cost, sufficiently high-resolution technique, Optical Coherence Tomography (OCT) to perform fracture analysis by obtaining the topography of metallic surfaces. Several metals have been considered in this study: low soft carbon steels, lamellar graphite cast iron, an antifriction alloy, high-quality rolled steel, stainless steel, and ductile cast iron. An in-house developed Swept Source (SS) OCT system, Master-Slave (MS) enhanced is used, and height profiles of the samples’ surfaces were generated. Two configurations were used: one where the dimension of the voxel was 1000 μm³ and a second one of 160 μm³—with a 10 μm and a 4 μm transversal resolution, respectively. These height profiles allowed for concluding that the carbon steel samples were subject to ductile fracture, while the cast iron and antifriction alloy samples were subjected to brittle fracture. The validation of OCT images has been made with SEM images obtained with a 4 nm resolution. Although the OCT images are of a much lower resolution than the SEM ones, we demonstrate that they are sufficiently good to obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures—especially with the higher resolution MS/SS-OCT system. The investigation is finally extended to the most useful case of fatigue fracture of metals, and we demonstrate that OCT is able to replace SEM for such investigations as well. Full article

(This article belongs to the Special Issue Fracture Behaviour of Innovative Materials under Different Enviromental Conditions)

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16 pages, 19842 KiB

Open AccessArticle

Fracture Energy and Fracture Morphology after Three-Point Bending Test of Welded Joints Made of Cast Steel Designed for Use in Power Sector, with and without the Addition of Rare Earth Metals

by Justyna Kasińska and Andrzej Skrzypczyk

Metals 2018, 8(2), 115; https://doi.org/10.3390/met8020115 - 07 Feb 2018

Cited by 1 | Viewed by 6027

Abstract

The paper reports the three-point bending test results of welded joints. The joints were made of chromium-molybdenum cast steel designed for the use at elevated temperatures. TIG (tungsten inert gas) welding technique was used. The fracture energy for particular joint zones and the [...] Read more.

The paper reports the three-point bending test results of welded joints. The joints were made of chromium-molybdenum cast steel designed for the use at elevated temperatures. TIG (tungsten inert gas) welding technique was used. The fracture energy for particular joint zones and the stretch zone width (SZW) under the notch bottom were determined in a qualitative fracture toughness assessment. Fracture surface morphology was analyzed. The stretch zone measurement indicated a qualitative relationship between its width and the values of fracture energy. The results confirmed the influence of the modification on the character of fracture and the portions of brittle and ductile fracture in particular areas of welded joints. Full article

(This article belongs to the Special Issue Fracture Behaviour of Innovative Materials under Different Enviromental Conditions)

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18628 KiB

Open AccessArticle

Corrosion Fatigue of Fine Grain Mg-Zn-Zr and Mg-Y-Zn Alloys

by Mikhail Linderov, Evgenii Vasilev, Dmitry Merson, Mikhail Markushev and Alexei Vinogradov

Metals 2018, 8(1), 20; https://doi.org/10.3390/met8010020 - 31 Dec 2017

Cited by 12 | Viewed by 4954

Abstract

Corrosion fatigue data for magnesium alloys are still scarce. The present communication reports the results of microstructural investigations and fatigue testing of the fine grain Mg-Zn-Zr (ZK60) alloy after multiaxial isothermal forging and of the hot extruded Mg-Y-Zn (WZ21) alloy in air and [...] Read more.

Corrosion fatigue data for magnesium alloys are still scarce. The present communication reports the results of microstructural investigations and fatigue testing of the fine grain Mg-Zn-Zr (ZK60) alloy after multiaxial isothermal forging and of the hot extruded Mg-Y-Zn (WZ21) alloy in air and in the 0.9% NaCl water solution. Both of the alloys demonstrate a very good high-cycle fatigue performance in air. However, the significant drop of fatigue resistance is observed in the corrosive environment. Results are discussed from perspectives of potential applications and future studies. Full article

(This article belongs to the Special Issue Fracture Behaviour of Innovative Materials under Different Enviromental Conditions)

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10124 KiB

Open AccessArticle

Fracture Toughness Prediction under Compressive Residual Stress by Using a Stress-Distribution T-Scaling Method

by Toshiyuki Meshii and Kenichi Ishihara

Metals 2018, 8(1), 6; https://doi.org/10.3390/met8010006 - 25 Dec 2017

Cited by 2 | Viewed by 8888

Abstract

The improvement in the fracture toughness J_c of a material in the ductile-to-brittle transition temperature region due to compressive residual stress (CRS) was considered in this study. A straightforward fracture prediction was performed for a specimen with mechanical CRS by using the [...] Read more.

The improvement in the fracture toughness J_c of a material in the ductile-to-brittle transition temperature region due to compressive residual stress (CRS) was considered in this study. A straightforward fracture prediction was performed for a specimen with mechanical CRS by using the T-scaling method, which was originally proposed to scale the fracture stress distributions between different temperatures. The method was validated for a 780-MPa-class high-strength steel and 0.45% carbon steel. The results showed that the scaled stress distributions at fracture loads without and with CRS are the same, and that J_c improvement was caused by the loss in the one-to-one correspondence between J and the crack-tip stress distribution. The proposed method is advantageous in possibly predicting fracture loads for specimens with CRS by using only the stress–strain relationship, and by performing elastic-plastic finite element analysis, i.e., without performing fracture toughness testing on specimens without CRS. Full article

(This article belongs to the Special Issue Fracture Behaviour of Innovative Materials under Different Enviromental Conditions)

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46062 KiB

Open AccessArticle

Fracture Resistance of 14Cr ODS Steel Exposed to a High Temperature Gas

by Anna Hojna, Jan Michalicka, Hynek Hadraba, Fosca Di Gabriele, Jan Duchon, Lucia Rozumova and Roman Husak

Metals 2017, 7(12), 560; https://doi.org/10.3390/met7120560 - 12 Dec 2017

Cited by 2 | Viewed by 4348

Abstract

This paper studies the impact fracture behavior of the 14%Cr Oxide Dispersion Strengthened (ODS) steel (ODM401) after high temperature exposures in helium and air in comparison to the as-received state. A steel bar was produced by mechanical alloying and hot-extrusion at 1150 °C. [...] Read more.

This paper studies the impact fracture behavior of the 14%Cr Oxide Dispersion Strengthened (ODS) steel (ODM401) after high temperature exposures in helium and air in comparison to the as-received state. A steel bar was produced by mechanical alloying and hot-extrusion at 1150 °C. Further, it was cut into small specimens, which were consequently exposed to air or 99.9% helium in a furnace at 720 °C for 500 h. Impact energy transition curves are shifted towards higher temperatures after the gas exposures. The transition temperatures of the exposed states significantly increase in comparison to the as-received steel by about 40 °C in He and 60 °C in the air. Differences are discussed in terms of microstructure, surface and subsurface Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) observations. The embrittlement was explained as temperature and environmental effects resulting in a decrease of dislocation level, slight change of the particle composition and interface/grain boundary segregations, which consequently affected the nucleation of voids leading to the ductile fracture. Full article

(This article belongs to the Special Issue Fracture Behaviour of Innovative Materials under Different Enviromental Conditions)

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15932 KiB

Open AccessArticle

Effect of Ultrasonic Surface Impact on the Fatigue Behavior of Ti-6Al-4V Subject to Simulated Body Fluid

by Xiaojian Cao, Xiaoli Xu, Chong Wang, Youngshik Pyoun and Qingyuan Wang

Metals 2017, 7(10), 440; https://doi.org/10.3390/met7100440 - 18 Oct 2017

Cited by 10 | Viewed by 5130

Abstract

The effect of ultrasonic nanocrystal surface modification (UNSM) on the fatigue behavior of Ti6Al4V (TC4) in simulated body fluid (SBF) was investigated. UNSM with the condition of a static load of 25 N, vibration amplitude of 30 μm and 36,000 strikes per unit [...] Read more.

The effect of ultrasonic nanocrystal surface modification (UNSM) on the fatigue behavior of Ti6Al4V (TC4) in simulated body fluid (SBF) was investigated. UNSM with the condition of a static load of 25 N, vibration amplitude of 30 μm and 36,000 strikes per unit produced about 35 μm surface severe plastic deformation (SPD) layers on the TC4 specimens. One group was treated with a hybrid surface treatment (UNSM + TiN film). UNSM technique improves the micro hardness and the compressive residual stress. The surface roughness is increased slightly, but it can be remarkably improved by the TiN film. The fatigue strength of TC4 is improved by about 7.9% after UNSM. Though the current density of corrosion is increased and the pitting corrosion is accelerated, UNSM still improved the fatigue strength of TC4 after pre-soaking in SBF by 10.8%. Interior cracks initiate at the deformed carbide and oxide inclusions due to the ultrasonic impacts of UNSM. Corrosion products are always observed at the edge of fracture surface to both interior cracks and surface cracks. Coating a TiN film on the UNSMed surface helps to improve the whole properties of TC4 further. Full article

(This article belongs to the Special Issue Fracture Behaviour of Innovative Materials under Different Enviromental Conditions)

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12853 KiB

Open AccessArticle

Behavior of the Steel T91 under Multi Axial Loading in Contact with Liquid and Solid Pb

by Fosca Di Gabriele, Anna Hojna, Michal Chocholousek and Jakub Klecka

Metals 2017, 7(9), 342; https://doi.org/10.3390/met7090342 - 04 Sep 2017

Cited by 12 | Viewed by 4683

Abstract

In this work, the conditions for the occurrence of Liquid Metal Embrittlement (LME) in the ferritic-martensitic steel T91 in contact with lead, Pb, were examined. Slow tensile tests with notched specimens revealed that in a temperature range close to the melting point of [...] Read more.

In this work, the conditions for the occurrence of Liquid Metal Embrittlement (LME) in the ferritic-martensitic steel T91 in contact with lead, Pb, were examined. Slow tensile tests with notched specimens revealed that in a temperature range close to the melting point of Pb, the steel is sensitive to LME (350–400 °C) and to Solid Metal Induced Embrittlement (SMIE) (300 °C). The cracking was stimulated by wetting (using a chemical flux) and the notch effect. It was found that the multi axial stresses state and the high level of plastic strain in front of the notch were the key factors triggering crack initiation. Full article

(This article belongs to the Special Issue Fracture Behaviour of Innovative Materials under Different Enviromental Conditions)

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