Raman analyses of residual stress in diamond thin films grown on Ti6Al4V alloy

Abstract

The stress evolution in diamond films grown on Ti6Al4V was investigated in order to develop a comprehensive view of the residual stress formation. Residual stress is composed of intrinsic stress induced during diamond film growth and extrinsic stress caused by the different thermal expansion coefficients between the film and substrate. In the coalescence stage it has been observed that the residual stress is dominated by the microstructure, whereas on continuous films, the thermal stress is more important. In this work diamond thin films with small grain size and good size and good quality were obtained in a surface wave-guide microwave discharge, the Surfatron system, with a negative bias voltage applied between the plasma shell and substrate. For above of -100V applied bias, the ratio of carbon sp³/sp² bond may increase and the nucleation rate increase arising the high value at the -250V applied bias. Stress measurements and sp³ content in the film were studied by Raman scattering spectroscopy. The total residual stress is compressive and varied from -1.52 to -1.48 GPa between 0 and -200 V applied bias, respectively, and above the -200 V, the compressive residual stress increased drastically to -1.80 GPa. The diamond nucleation density was evaluated by top view SEM images

Raman imaging and stress quantification in self‐assembled graphene oxide fiber ‘Latin Letters’

“…This implies that elastic constants also change depending on the structure and morphology of the material as it is related to stress coefficients. Hence, we observed that the calculated results for GO letters are more comparable to this model in our case. The detailed theoretical framework proposed by Sakata et al for calculating biaxial stress in graphitic fibers is provided in the Supporting Information.…”

“…However, from an alternative approach, we have also computed the biaxial stress for all the fibers at junction points using the theoretical model proposed by Sakata et al , which is a well‐known framework to calculate biaxial stress in graphitic fiber. Using A = −1.44 × 10 7 cm −2 and graphite elastic constants S 11 = 0.98 × 10 −12 Pa −1 and S 12 = −0.16 × 10 −12 Pa −1 and respective values of ω 0,a and ω 0,j for three ‘letters’, the calculated stress ( σ ) is estimated to be almost half to the model used by Azevedo et al . This discrepancy can be attributed to the value of the stress coefficient, which is almost double for graphite fiber compared with the experimental stress coefficient findings for GO in Xu and Cheng under pressure‐induced Raman shift measurement.…”

“…From the G band spectral data, Γ a / Γ j and Δ ω were found to be ~0.91 and 3 cm −1 respectively, in ‘G’ fiber. Computation of relative residual biaxial stress induced within the system can be calculated by using an empirical formula from Raman shift given by , where Δ ω is the Raman shift from the original position, and α cm − 1 /GPa is the Raman shift/GPa (pressure coefficient), which is taken as 3.8 cm −1 /GPa that has been reported recently for GO . The sign of Δ ω is ‘+’ for Raman shift to higher wavenumber implying compressive stress while ‘−’ is for Raman shift to lower wavenumber implying tensile stress .…”

“…The elastic constants given by Sakata et al are preferred for biaxial stress calculations in pure graphene‐based systems. However, the model discussed by Azevedo et al is generally applied for the experimentally prepared materials to calculate stress. More often stress coefficient is obtained by observing the Raman shift in pressure ambient for different materials.…”

Filmes de nanodiamantes para aplicações em sistemas eletroquímicos e tecnologia aeroespacial

“…Algumas destas aplicações industriais incluem o uso destes filmes na fabricação de revestimentos duros que possuem baixo coeficiente de fricção e excelentes propriedades de desgaste 98,99 , dispositivos emissores de elétrons 96,100 e revestimentos resistentes a impacto [101][102][103] . A nanocristalinidade destes filmes é o resultado de um novo tipo de crescimento e mecanismos de nucleação, que envolvem a inserção do carbono (dímero) nas ligações carbono-carbono e carbono-hidrogênio, resultando em uma taxa de nucleação em torno de 10 10 cm 79 , que fornece propriedades mecânicas, elétricas e ópticas com características únicas aos filTipicamente, a mistura gasosa utilizada na obtenção dos filmes de diamante microcristalinos ou nanocristalinos costuma ser hidrogênio e metano 80,100,101,103,106,114,116 . Entretanto, na obtenção de nanofilmes, alguns autores têm usado outras composições contendo argônio, hidrogênio e metano 83,99,109 ou hélio, hidrogênio e metano 50,81,82 .…”