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Examining, Analyzing, Interpreting, and Understanding the Fracture Resistance of High Entropy Alloys
Published in T.S. Srivatsan, Manoj Gupta, High Entropy Alloys, 2020
The HEAs with a single bcc phase can fail by either transgranular cleavage or intergranular separation. Since both processes involve very limited plasticity, the associated fracture mechanisms in bcc HEAs are not expected to be as complex as in fcc HEAs. Like all other materials, the cleavage in bcc HEAs also results from the breakage of weaker bonds between atoms on certain crystallographic planes. On the other hand, the intergranular fracture may be caused by the segregation of impurities at grain boundaries.
Fracture, fatigue, and creep of metals
Published in Gregory N. Haidemenopoulos, Physical Metallurgy, 2018
Mechanisms of ductile and brittle fracture. There is a considerable difference between the two types of fracture. Brittle fracture takes place by cleavage along specific crystallographic planes, by breaking atomic bonds, e.g., the {100} planes in iron. Cleavage results in a flat fracture in the scale of a grain. In a polycrystalline material, however, the neighboring grains have different orientations and the advancing crack changes direction from grain to grain as it propagates along the cleavage planes. This results in transgranular fracture, which corresponds to a multifaceted fracture surface (Figure 9.1). A fresh fracture surface is usually shiny due to the reflection of light from the cleavage planes. The crack can also propagate along the grain boundaries of the metal resulting in intergranular fracture, as shown in Figure 9.2. Intergranular fracture is usually caused by the weakening of grain boundaries due to the segregation of certain elements, such as phosphorous and sulfur in steels. Carbide precipitation at the grain boundaries, as in the sensitization of austenitic stainless steels, can also cause brittle intergranular fracture. Finally creep fracture at high temperatures can also be intergranular.
Fracture Mechanisms in Metals
Published in T.L. Anderson, Fracture Mechanics, 2017
Figure 5.1 schematically illustrates three of the most common fracture mechanisms in metals and alloys. (A fourth mechanism, fatigue, is discussed in Chapter 10.) Ductile materials (Figure 5.1a) usually fail as the result of nucleation, growth, and coalescence of microscopic voids that initiate at inclusions and second-phase particles. Cleavage fracture (Figure 5.1b) involves separation along specific crystallographic planes. Note that the fracture path is transgranular. Although cleavage is often called brittle fracture, it can be preceded by large-scale plasticity and ductile crack growth. Intergranular fracture (Figure 5.1c), as its name implies, occurs when the grain boundaries are the preferred fracture path in the material.
Microstructure evolution and mechanical properties of low-silicon cast aluminium alloys with varying Mn contents
Published in Philosophical Magazine, 2021
Dongling Qian, Tengfei Cheng, Wenjie Gao, Yitao Yang
The fracture surfaces of the as-cast alloys containing 0, 0.5%, 0.8% Mn are shown in Figure 8, in which the intergranular fracture, crack and tear ridges respectively are marked red, blue and yellow arrows. The fracture characteristics of alloys with different Mn content reveal that with the increase of Mn content from 0 to 0.8%, the fracture modes of alloys changed from intergranular + cleavage fracture to intergranular + quasi-cleavage fracture. Vast smooth grain interfaces (marked by red arrows) and cleavage planes were observed on the fracture surface of the alloy without Mn, and the cracks extended along the grain boundaries, showing obvious brittle fracture characteristics. As the addition of Mn, the morphology and size of Fe-rich phase were improved, reducing the possibility of crack initiation. The as-cast alloy containing 0.5% Mn showed ductile fracture. Under the combined action of the refinement of Si particles and intermetallic compounds avoiding the crushing and debonding of hard particles effectively and matrix softening due to the consumption of Mg atoms in the matrix caused by the formation of π-Fe phase, the initiation and propagation of cracks mainly relied on the development of void caused by plastic strain accumulation within grains or at grain boundaries (marked by blue arrow in Figure 8(e)), and cleavage planes displayed marked necking and a rough appearance. The 0.8% Mn modified alloy exhibited a mixed mode of brittle intergranular fracture and ductile transgranular fracture. The fracture surface reappeared numerous traces of intergranular fracture, and the polyhedral morphology of the grains was observed. This was because the formation of the coarse π-Fe phase increased the location of stress concentration and crack initiation. The presence of tear ridges (marked by the yellow arrow in Figure 8(c,f)) indicated further softening of the matrix.
Microstructure and properties of CPED thermal protective ceramic coating toughened by ZrO2 nanorods on Al–Si alloy
Published in Surface Engineering, 2021
Ping Wang, Qun Ma, Xiaomin Chen, Chunqing Zhang
Research shows [25] that intergranular fracture has higher toughness than transgranular fracture, which is due to the smaller crack growth resistance of transgranular fracture at the grain boundary. For intergranular fracture, when the crack propagates to a grain surface, it must turn to a new direction and present a break line, which increases the resistance of crack propagation.
Heat generation and steel fragment effects on friction stir welding of aluminum alloy with steel
Published in Materials and Manufacturing Processes, 2023
Pankaj Kaushik, Dheerendra Kumar Dwivedi
Fractured surfaces of joint 9 (708/280) are presented in Fig. 12. The joint failed from the stir zone toward the aluminum alloy side. The failure mechanism is mixed, with some areas failing by ductile (dimple) fracture and others failing via brittle (intergranular) fracture.