arXiv subjects

T. Polcar

Publications and source records attributed to T. Polcar.

3 recordsLinked to original sources

arXiv2026

Physics-Constrained Inverse Estimation of Irradiation-Induced Strain in He-H Ion-Implanted 4H-SiC Using Nanoindentation and Finite Element Modeling

Nanoindentation is widely used to evaluate the mechanical properties of irradiated materials however its potential for quantifying irradiation induced subsurface strain remains underexplored. In this work, an integrated experimental numerical framework based on a physics constrained inverse modeling approach is employed to estimate the magnitude of a depth dependent irradiation induced strain distribution in single crystal 4H SiC following sequential He and H ion implantation. The approach combines depth sensing nanoindentation, finite element modeling FEM, and a simplex based inverse optimization routine to calibrate a physically motivated eigenstrain profile derived from ion damage simulations. The strain field is assumed to follow a lognormal distribution consistent with independently determined damage profiles SRIM, and is implemented in the FEM model through a depth dependent thermal expansion formulation. By minimizing the squared error between simulated and experimental force displacement curves, the peak tensile strain is estimated to be 0.91, accompanied by an effective Young s modulus of 310 GPa and a yield strength of 16.4 GPa. Independent validation using nano beam precession electron diffraction N PED confirms good agreement between the reconstructed and experimentally measured out of plane strain profiles in both magnitude and spatial distribution. The results demonstrate that nanoindentation, when combined with physics based inverse modeling, can provide a practical tool for quantifying irradiation-induced strain and residual stress in nuclear ceramics. This methodology offers a complementary approach to diffraction based techniques for assessing subsurface damage in ion irradiated materials relevant to advanced nuclear systems.

physics.app-ph↗

arXiv2017

Effects of layer thickness on the mechanical behavior of oxidation-strengthened Zr/Nb nanoscale multilayers

The mechanical behaviour and deformation mechanisms of magnetron-sputtered Zr/Nb nanoscale multilayers were analysed as a function of the periodicity (L = 10 and 75 nm) and annealing time at 350C (2-336 hrs). The strength of the as-deposited multilayers was independent of the layer thickness and it was controlled by the co-deformation of the Zr and Nb layers. Annealing led to transformation of the Zr layers into ZrO2 after a few hours, while the Nb layers oxidised at a much slower rate. The volumetric expansion associated with the oxidation led to the formation of cracks at the interfaces and within the ZrO2 layers for the multilayers with L = 75 nm but not in the case of L = 10 nm. The nanoindentation hardness increased significantly after annealing due to the contribution of the residual stresses associated with the volume increase due to oxidation and to the higher strength of the oxides. The strength increase after annealing, as measured by micropillar compression tests, was smaller than that measured by nanoindentation, as it did not include the contribution of the residual stresses, which were relieved during micropillar fabrication. The nanolaminate with L = 10 nm presented the highest strength and toughness as damage during oxidation was suppressed, and a deformation mechanism controlled by the formation of shear bands.

cond-mat.mtrl-sci↗

arXiv2016

Selective oxidation-induced strengthening of Zr/Nb nanoscale multilayers

The paper presents a new approach, based on controlled oxidation of nanoscale metallic multilayers, to produce strong and hard oxide/metal nanocomposite coatings with high strength and good thermal stability. The approach is demonstrated by performing long term annealing on sputtered Zr/Nb nanoscale metallic multilayers and investigating the evolution of their microstructure and mechanical properties by combining analytical transmission electron microscopy, nano-mechanical tests and finite element models. As-deposited multilayers were annealed at 350 C in air for times ranging between 1 - 336 hours. The elastic modulus increased by approx. 20% and the hardness by approx. 42% after 15 hours of annealing. Longer annealing times did not lead to changes in hardness, although the elastic modulus increased up to 35% after 336 hrs. The hcp Zr layers were rapidly transformed into monoclinic ZrO2 (in the first 15 hours), while the Nb layers were progressively oxidised, from top surface down towards the substrate, to form an amorphous oxide phase at a much lower rate. The sequential oxidation of Zr and Nb layers was key for the oxidation to take place without rupture of the multi-layered structure and without coating spallation, as the plastic deformation of the metallic Nb layers allowed for the partial relieve of the residual stresses developed as a result of the volumetric expansion of the Zr layers upon oxidation. Moreover, the development of residual stresses induced further changes in mechanical properties in relation to the annealing time, as revealed by finite element simulations.

cond-mat.mtrl-sci↗