Environmental reactions and their effects on mechanical behavior of metallic materials. Technical progress report, February 1, 1980-January 31, 1981 (original) (raw)
Related papers
1976
During the past contract year, new results have been obtained in two ongoing project areas: (1) surface oxide softening and solute gradients in niobium and tantalum, and (2) mechanical properties of Nb-H, Nb-D, and Nb-O-H alloys. The important results include: (a) characterization of the large softening and ductilizing effect of niobxum and tantalum caused by thin (50-100 nm) surface oxide films; (b) determination of the role of interstitial impurities in the strengthening and ductility changes caused by hydrogen and deuterium in niobium; and (c) observation of hydride precipitate softening in niobium. l
1979
A number of defect sites interact significantly enough with hydrogen in ferrous alloys to act as traps under circumstances in which the material exhibits hydrogen-induced loss of ductility. These sites include point defects (solute atoms, vacancies), dislocations (edge and screw), interfaces and surfaces (grain boundaries, particle-matrix interfaces, cracks, external surfaces), and volume defects (voids, second phase particles). Experiments performed under controlled conditions involving careful microstructural characterization have generated quantitative estimates of number densities, binding energies and saturabilities of defects, which in turn can be used to imply probable susceptibilities to hydrogen embrittlement.' Current information on hydrogen-defect interactions is reviewed and applied to results on the nature of hydrogen-assisted crack paths in a high strength steel. It is shown that both the primary and secondary crack paths can be explained in terms of the types of microstructural traps that predominate in a given material.
1977
A number of defect sites interact significantly enough with hydrogen in ferrous alloys to act as traps under circumstances in which the material exhibits hydrogen-induced loss of ductility. These sites include point defects (solute atoms, vacancies), dislocations (edge and screw), interfaces and surfaces (grain boundaries, particle-matrix interfaces, cracks, external surfaces), and volume defects (voids, second phase particles). Experiments performed under controlled conditions involving careful microstructural characterization have generated quantitative estimates of number densities, binding energies and saturabilities of defects, which in turn can be used to imply probable susceptibilities to hydrogen embrittlement.' Current information on hydrogen-defect interactions is reviewed and applied to results on the nature of hydrogen-assisted crack paths in a high strength steel. It is shown that both the primary and secondary crack paths can be explained in terms of the types of microstructural traps that predominate in a given material.
V. DISCUSSION OF RESULTS 88 A. Internal Friction Measurements 88 1. Effect of oxygen on Nb-V alloys 88 2. Trapping energy calculations 94 3. Elastic versus chemical interactions 99 4. Appearance of additional peak 106 5. Effect of oxygen and hydrogen on Nb and Nb-10 at% V alloys 106 B. Tensile Tests 110 1. Effect of oxygen on Nb-10 atjf V alloy 110 2. Combined effects of oxygen and hydrogen on Nb-10 at% V alloy 113 a. Alloy softening 113 b. Strengthening effect 115 c. Ductility d.
Internal friction study of environmental effects on metals and alloys
Journal of Alloys and Compounds
The internal friction method was applied for studying structural changes occurring in bulk metal due to its interaction with the environment. It was shown that the active dissolution of metal or its oxidation is accompanied by the generation of non-equilibrium vacancies. Diffusive transfer of vacancies into the bulk causes considerable rearrangements of the defect structure of the crystal and, therefore, changes in its anelastic response. Environmental effects have been studied in pure copper subjected to oxidation in a 0.3 N solution of NaNO. Such an interaction resulted in the formation of Hasiguti peaks. A similar effect was found in admiralty brass after 2 oxidation in hot tap water, resulting in selective dissolution of zinc. Low-temperature internal friction peaks were also found in the range 150-200 K in Al-5 Mg industrial alloy subjected to active dissolution in 0.05 N KOH solution. The results obtained are discussed in terms of the applicability of the internal friction method for predicting the susceptibility of metals and alloys to environmentally assisted cracking.
Interplay between microstructural evolution and tribo-chemistry during dry sliding of metals
Friction, 2019
Understanding the microstructural and tribo-chemical processes during tribological loading is of utmost importance to further improve the tribological behavior of metals. In this study, the friction, wear and tribo-chemical behavior of Ni with different initial microstructures (nanocrystalline, bi-modal, coarse-grained) is investigated under dry sliding conditions. In particular, the interplay between frictional response, microstructural evolution and tribo-oxidation is considered. Friction tests are carried out using ball-on-disk experiments with alumina balls as counter-bodies, varying the load between 1 and 5 N. The microstructural evolution as well as the chemical reactions beneath the samples' surface is investigated by means of cross-sections. The samples with finer microstructures show a faster run-in and lower maximum values of the coefficient of friction (COF) which can be attributed to higher oxidation kinetics and a higher hardness. It is observed that with increasing sliding cycles, a stable oxide layer is formed. Furthermore, initially coarse-grained samples show grain refinement, whereas initially finer microstructures undergo grain coarsening converging towards the same superficial grain size after 2,000 sliding cycles. Consequently, the experimental evidence supports that, irrespective of the initial microstructure, after a certain deformation almost identical steady-state COF values for all samples are achieved.
Anelastic relaxation processes due oxygen in Nb–3.1 at.% Ti alloys
Materials Science and Engineering A, 2004
In the last 50 years several studies have been made to understand the relaxation mechanisms of the heavy interstitial atoms present in transition metals and their alloys. Internal friction measurements have been carried out in a Nb-Ti alloy containing 3.1 at.% of Ti produced by the Materials Department of Chemical Engineering Faculty of Lorena (Brazil), with several quantities of oxygen in solid solution using a torsion pendulum. These measurements have been performed by a torsion pendulum in the temperature range from 300 to 700 K with an oscillation frequency between 0.5 and 10 Hz. The experimental results show complex internal friction spectra that have been resolved, into a series of Debye peaks corresponding to different interactions. For each relaxation process it was possible to obtain the height and temperature of the peak, the activation energy and the relaxation time of the process.
Slow strain-rate embrittlement of niobium by Oxygen
Metallurgical Transactions A, 1976
The embrittlement of niobium by oxygen has been studied over the temperature range from 77 to 1100 K using tensile specimens containing between 0.09 and 2.31 at. pct oxygen. A slow strain-rate embrittlement was observed in specimens containing more than 0.5 at. pct oxygen that occurred inside the approximate temperature range from 500 to 1000 K. In analogy with the slow strain-rate embrittlement due to hydrogen, a ductileto-brittle-to-ductile fracture transition was observed; the ductility (reduction in area) decreased with decreasing strain-rate: the ductility decreased with increasing oxygen concentration; and a fracture morphology involving both intergranular and transgranular modes was observed. The transgranular mode, which was the predominant one, resembled cleavage.
Materials, 2019
Fatigue is a dominant failure mechanism of several engineering components. One technique for increasing the fatigue life is by inducing surface residual stress to inhibit crack initiation. In this review, a microstructural study under various bulk (such as severe plastic deformation) and surface mechanical treatments is detailed. The effect of individual microstructural feature, residual stress, and strain hardening on mechanical properties and fatigue crack mechanisms are discussed in detail with a focus on nickel-based superalloys. Attention is given to the gradient microstructure and interface boundary behavior for the mechanical performance. It is recommended that hybrid processes, such as shot peening (SP) followed by deep cold rolling (DCR), could enhance fatigue life. The technical and scientific understanding of microstructural features delineated here could be useful for developing materials for fatigue performance.