Small-scale analysis of brittle-to-ductile transition behavior in pure tungsten

Tungsten as a material exhibits broad and increasingly important applications;however,the characterization of its ductile-to-brittle transition(BDT)is currently limited to large-scale scenarios and destructive testing.In this study,we overcome this challenge by implementing small-scale techniques to provide a comprehensive understanding of the BDT behavior of pure tungsten.In order to predict the failure mode at various temperature ranges,the practical fracture analysis diagram has been proposed to describe the resistance to shear flow and cracking behavior with temperature.High temperature nano-indentation tests have provided the inherent mechanical responses corresponding to the maximum shear stress at various temperatures,which is required for dislocation activities in an atomic scaled activation volume.On one hand,atomistic simulations have provided the temperature dependence of brittle fracture stress,where the atomic bonds break due to intergranular or intragranular fracture.We considered four tungsten specimens having various microstructures prepared using different processing conditions of cold-rolling and post-annealing,and their BDT ranges were inferred using the obtained fracture analysis diagram with the statistical data processing.The fracture analysis diagram of each specimen obtained were compared with the direct observation of fracture responses in macroscopic mechanical tests,which conclusively indicated that the small-scale inherent mechanical properties are greatly relevant to the macroscopic BDT behavior in pure tungsten.Based on the BDT estimations by small-scale characterization,we provided further insights into the factors affecting the BDT behavior of tungsten,focusing on the contributions of different types of dislocations.

A DFT study on brittle-to-ductile transition of D022-TiAl3 using multi-doping and strain-engineered effects

In this work,the thermodynamic,mechanical properties and electronic behaviors of D022-TiAl3 doped with W and 15 groupⅣM(M=C,Ge,Pb,Si and Sn)dopants are investigated by DFT methods.We established that ductility can be improved using multi-doping approach and revealed the mechanisms behind such brittle-to-ductile transition.In addition,it is found that there is linearity between changes in Young’s modulus and tensile/compre s sive strain ratio.An alternate insight into brittle-to-ductile transition during ductile mode cutting of brittle materials is proposed.

Brittle-to-ductile transition in Ti–Pt intermetallic compounds

Phase transformation changes numerous properties of materials. Ti–Pt alloys have received much interest because of high martensitic transformation temperature. However, the intrinsic brittleness of these intermetallic compounds with low crystal symmetry and complicated phase structure limit their applications,especially when composition deviates from stoichiometry ratio. By performing in situ heating high-resolution scanning transmission electron microscopy experiment and micro-mechanical testing on Ti-35 at% Pt that contained majorly Ti3Pt and αTiPt phases, it was found that precipitating herringbone twinned αTiPt islands within Ti3Pt could occur upon heating, significantly refining mixed-phase structure. The refinement of multi-intermetallic mixed-phase structure endowed brittle material with remarkable capacity for plastic deformation and strain hardening. The plastic deformation mechanisms include phase transformation upon yielding and dislocation slips during hardening, which rarely occurs in intermetallic compounds with low symmetry. The strong interaction between different deformation modes even caused nano-crystallization along slip bands. The results demonstrate that brittle-toductile transition in intermetallic compounds can be achieved by tuning mixed-phase structure through phase transformations.

BDT and Creep Behaviors of NiAl-25 at.pct Cr Alloy at Various Temperatures

Brittle-to-ductile transition （BDT） behavior and creep behavior of extruded NiAl-25Cr alloy at elevated temperatures were investigated. The results reveal that the alloy exhibits obvious BDT behavior with the increase in temperature and BDT temperature （BDTT） is sensitive to initial strain rate. When the initial strain rate increases by two orders of magnitude, BDTT has an increase of approximate 80 K. The creep data in the temperature range of 1073～1123 K reveal two distinct regions of creep behavior in this material. At lower temperature, the creep characteristics are consistent with structural controlled creep process where creep deformation is controlled by dislocation climb. At higher temperature, the creep characteristics are consistent with mobility-controlled deformation where viscous glide of dislocations controls creep. The apparent activation energy determined by creep in both regions exceeds the value for lattice self-diffusion in NiAl by a considerable amount. This can be explained in terms of the simultaneous deformation of second phase particles （γ′-Ni3Al and a-Cr phase） along NiAl matrix during creep.

Effect of structural vacancies on lattice vibration,mechanical,electronic,and thermodynamic properties of Cr5BSi3

In recent years,transition metal silicides have become the potential high temperature materials.The ternary silicide has attracted the attention of scientists and researchers.But their inherent brittle behaviors hinder their wide applications.In this work,we use the first-principles method to design four vacancy defects and discuss the effects of vacancy defects on the structural stability,mechanical properties,electronic and thermodynamic properties of hexagonal Cr;BSi;silicide.The data of lattice vibration and thermodynamic parameters indicate that the Cr;BSi;with different atomic vacancies can possess the structural stabilities.The different atomic vacancies change the mechanical properties and induce the Cr;BSi;to implement the brittle-to-ductile transition.The shear deformation resistance and volume deformation resistance of Cr;BSi;are weakened by different vacancy defects.But the brittleness behavior is remarkably improved.The structural stability and brittle-to-ductile transition of Cr;BSi;with different vacancies are explored by the electronic structures.Moreover,the thermal parameters indicate that the Cr;BSi;with vacancies exhibit different thermodynamic properties with temperature rising.

EFFECTS OF DISLOCATION CONFIGURATION,CRACK BLUNTING AND FREE SURFACES ON THE TRIGGERING LOAD OF DISLOCATION SOURCES

The effects of dislocation configuration, crack blunting and free surfaces on the triggering load of dislocation sources in the vicinity of a crack or a wedge tip subjected to a tensile load in the far field are investigated. An appropriate triggering criterion for dislocation sources is proposed by considering the configurational forces acting on each dislocation. The triggering behaviors of dislocation sources near the tips of a crack and a wedge are compared. It is also found that the blunting of crack tip and the presence of free surfaces near the crack or the wedge have considerable influences on the triggering load of dislocation sources. This study might be of significance to gaining a deeper understanding of the brittle-to-ductile transition of materials.