Showing 5 results for Fractography
S. Gholami Shiri, Y. Palizdar, . A. Jenabali Jahromi, Eduardo F. de Monlevade,
Volume 15, Issue 3 (9-2018)
Abstract
The relation between microstructure and the fracture mechanisms of δ-TRIP steel with different Nb-content has been investigated using complementary methods of light microscopy, SEM, EDS, EBSD, X-ray phase analysis and tensile test. The results revealed a close dependency between the presences of constitutive phases i.e. ferrite, bainite, retained austenite and martensite and the mode and characteristics of fracture. All samples revealed almost different fractography pattern which could be associated to the effect of Nb microalloying element. The different fractography patterns were consisted of dimple rupture, riverside and Wallner lines pattern. The proportion of the cleavage fracture in comparison of dimple rapture increased by increasing the Nb-content due to the increase of primary martensite in the microstructure.
Mitra Ghannadi, Hediye Hosseini, Bagher Mohammad Sadeghi, Bahman Mirzakhani, Mohammad Tahaaha Honaramooz,
Volume 18, Issue 3 (9-2021)
Abstract
The objective of the present paper is to investigate the effects of rapid heating and cryogenic cooling on on the microstructure and tensile properties of Al-Cu-Mg. The specimens were subjected to three heat treatment cycles in which the Infrared heating (IR) were used as the heating medium at the ageing stage, and the liquid nitrogen and water were used as the quenching mediums. The ageing temperature and time were 190⁰C and from 2 hours to 10 hours, respectively.The results indicated that by using IR at the ageing stage, the hardening rate enhanced because the rapid heating via this method leads to faster diffusion of the alloying elements. Moreover, the high density of nano-sized precipitates formed during ageingleads to higher strength and suitable ductility. Cryogenic treatment showed a negligible effect on both microstructure and tensile properties; however, it improved ductility. Overall, the combination of a high heating rate and cryogenic treatment led to the highest mechanical properties. SEM micrograph of the fracture surface of alloy demonstrated that in Cryogenic treatment+Artificial Ageing (CAA) condition, the surface had been fully covered by deep dimples in contrast to the Cryogenic treatment+Infrared Heating (CIR) and Water-Quench+ Infrared Heating (QIR) conditions which their dimples were shallow and also some facets were observed.
Mohammad Abankar, Hossein Arabi, Mohammad Taghi Salehi, Majid Abbasi,
Volume 20, Issue 1 (3-2023)
Abstract
The aims of this research were to evaluate the effects of different thermomechanical treatments on the microstructure and investigate some of the mechanical properties of a TWIP steel rich in Mn & Al. So, a block of a TWIP steel with nominal composition Fe-17.5Mn-1.36Al-0.8C was cast and then subjected to hot rolling followed by cold rolling and heat treatment. Cold rolling was performed before heat treatment in order to reduce the grain size and improve the tensile and fatigue properties. X-ray diffraction technique was used before and after the heat treatment to evaluate the possibility of any phase formation. No sign of martensitic transformation after cold deformation was observed. However, by increasing the amount of cold deformation, the number of mechanical twins and slip band increased resulted to an increase in hardness and strength. The best tensile and fatigue result were obtained after 47% thickness reduction and annealing at 715˚C for 10 min. Under these conditions, the mean grain size reduced from 138 to 9 μm resulted to an increase in yield strength from 395 to 510 MPa, and the fatigue life improvement from the mean life of 10200 for the cast sample to 21500 cycles for the treated sample, when these samples underwent fatigue tests at a stress range of 650 MPa and R=0. In addition, the diameter and depth of dimples in fracture surfaces decreased by reducing the grain size but the fracture mode was remained ductile and adequate plastic deformation occurred before failure.
Mahdi Behjati , Seyed Ali Asghar Akbari Mousavi , Yaser Vahidshad,
Volume 22, Issue 4 (12-2025)
Abstract
This work presents a comprehensive investigation of the high cycle fatigue behavior of Haynes 25 cobalt-based superalloy and its welds produced by pulsed continuous-wave (CW) laser welding. The alloy, manufactured through vacuum induction melting and electroslag remelting followed by rolling and annealing, exhibited a yield strength of 650 MPa, an ultimate tensile strength of 1050 MPa, and an outstanding elongation of 57% at room temperature. The fatigue limit was determined by test method as 200 MPa for lifetimes exceeding 10⁸ cycles, highlighting its excellent resistance to cyclic loading. For the weld zone, fabricated under optimized pulsed CW laser parameters, the yield and ultimate tensile strengths were 660 MPa and 965 MPa, respectively, with a fatigue limit of 175 MPa. Advanced microstructural analyses using OM, SEM, EBSD, and XRD revealed an austenitic FCC matrix with carbide precipitates, predominantly (W, Cr)₇C₃ and M₆C, decorating both the matrix and grain boundaries. Fatigue crack initiation in the base metal was associated with carbide clusters near the surface, while in the weld zone it was strongly linked to near-surface gas porosity defects. These findings not only establish fundamental fatigue benchmarks for Haynes 25 but also provide the first direct insights into the microstructural origins of fatigue damage in its laser-welded joints, thereby addressing a critical knowledge gap for its deployment in high-temperature and cyclic-loading environments.
Krishnakumar K, Rajamanickam M.r,
Volume 23, Issue 3 (9-2026)
Abstract
Track rollers used in bucket wheel excavators are subjected to repeated mechanical loading in an environment where abrasive particles, moisture and corrosive contaminants can accelerate surface deterioration. The present study examines the mechanical, electrochemical and tribological behaviour of GS‑42CrMo4V cast steel used for this application. The material w::as char::acterized through chemical composition analysis, microhardness measurement, tensile testing and fractographic examination. Its corrosion behaviour was further evaluated in 3.5 wt.% NaCl and acidic HCl and H₂SO₄ solutions using potentiodynamic polarization and electrochemical impedance spectroscopy, while three-body abrasion and reciprocating wear tests were carried out to assess its resistance to material loss under different contact conditions. The bottom roller exhibited an average microhardness of 430 HV, compared with 314.2 HV for the roller pin. Tensile and fractographic observations indicated good mechanical performance, although localized damage features were observed on the fractured surfaces. The electrochemical results showed that the material performed better in the neutral chloride solution than in the acidic media. In 3.5 wt.% NaCl, the corrosion current density and corrosion rate were 1.597 μA cm⁻² and 0.487 mpy, respectively, whereas the acidic solutions produced considerably higher corrosion activity. The wear tests confirmed that high hardness alone did not prevent material removal under abrasive and sliding contact. Abrasive action, plastic deformation and localized adhesive interactions contributed to surface degradation under the investigated conditions. The results therefore indicate that, despite its favourable hardness and mechanical characteristics, GS-42CrMo4V remains susceptible to degradation in aggressive acidic environments and under severe abrasive and sliding conditions. The observed behaviour points to the need for further improvement in material processing, surface condition, corrosion protection and the control of abrasive particle ingress. These findings provide a basis for understanding the service-related limitations of the material and for improving the durability of track rollers used in mining equipment.
