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Ti6Al4V ELI alloy is widely used for the fabrication of a wide range of load-bearing implants. Surface modification by laser shock processing (LSP) has demonstrated the capability to generate roughness of clinical interest, being the control of the surface and subsurface microstructural changes relevant to the intended applications. This work is aimed to compare the induced effects by scanning electron microscopy (SEM) and thermoelectric power (TEP) techniques to sense the subtle material variations such as local texture, increased dislocation density, hardening and residual stresses degree in a non-destructive way. For comparative purposes, synchrotron radiation X-ray diffraction (SR-XRD) experiments were also carried out to determine the residual stress state, The magnetic flux density (MFD) measurements demonstrate that the non-contact technique is very sensitive to the compressive residual stresses with increasing the severity of the laser treatment parameters, while the TEP contacting results are closely related to grain size, cracks, anisotropy, and work hardening., This work was partially supported by CONACYT (México) CB-256013. M.A. Montealegre is acknowledged by the surface modification of alloy.

This research work was focused on the laser peening surface process in a metallic Ti-6Al-4V biomaterial. The Ti-6Al- 4V samples were surface treated at different laser conditions varying parameters such as pulse density and wave length. Laser peening induced effects were evaluated by synchrotron radiation X-ray diffraction (SR-XRD) to determine the residual stress state; scanning electron microscopy (SEM) to assess microstructural changes and thermoelectric testing (TEP) to sense the subtle material variations such as local texture, increased dislocation density, hardening and residual stresses degree. The TEP measurements demonstrate that the non-contact technique is very sensitive to the compressive residual stresses with increasing the severity of the laser treatment parameters, while the TEP contact results are closely related to grain size, cracks, anisotropy, and work hardening.

Flat fatigue specimens of biomedical Ti6Al4V ELI alloy were surface-processed by high pressure waterjet peening (WJP) without abrasive particles using moderate to severe conditions that yield roughness values in the range of those obtained by commercial grit blasting (BL) with alumina particles. Fatigue behavior of WJP and BL specimens was characterized under cyclical uniaxial tension tests (R=0.1). The emphasis was put on a comparative analysis of the surface and subsurface induced effects and in their relevance on fatigue behavior. Within the experimental setup of this investigation it resulted that blasting with alumina particles was less harmful for fatigue resistance than abrasiveless WJP. BL specimens resulted in higher subsurface hardening and compressive residual stresses. Specimens treated with more severe WJP parameters presented much higher mass loss and lower compressive residual stresses. From the analysis performed in this work, it follows that, in addition to roughness, waviness emerges as another important topographic parameter to be taken into account to try to predict fatigue behavior. It is envisaged that optimization of WJP parameters with the aim of reducing waviness and mass loss should lead to an improvement of fatigue resistance., The authors acknowledge support from projects MINECO (MAT 2012-37736-C05-01 and MAT 2012-37782), HZB (BESSY, Proposal 14100041) and Comunidad de Madrid (Multimat Challenge S2013/MIT-2862). The CIBER of Bioingeniería, Biomateriales y Nanomedicina is supported by the ISCIII. Thanks are also due to Jesús Chao for his help with the tensile tests, Dr. Gaspar González-Doncel for his help with measurement of residual stresses, both from CENIM, and Alfredo Suárez from Tecnalia for his help with the waterjet processing. Naiara Gallardo and Edurne Laurín are greatfully acknowledged for their technical assistance, as well as the laboratory of Microscopy (A. García and A. Tomás).

We investigated a Ti6Al4V alloy modified by means of laser peening in the absence of sacrificial coatings. As a consequence of the temperature rise during laser focusing, melting and ablation generated an undulated surface that exhibits an important increase in the content of titanium oxides and OH- ions. Human mesenchymal stem cells and osteoblasts cultured on the oxidized alloy develop noticeable filopodia and lamellipodia. Their paxillin-stained focal adhesions are smaller than in cells attached to the untreated alloy and exhibit a marked loss of colocalization with the ends of actin stress fibers. An important imbalance of phosphorylation and/or dephosphorylation of the focal adhesion kinase is detected in cells grown on the oxidized alloy. Although these mechanisms of adhesion are deeply altered, the surface treatment does not affect cell attachment or proliferation rates on the alloy. Human mesenchymal stem cells cultured on the treated alloy in media containing osteogenic inducers differentiate towards the osteoblastic phenotype to a higher extent than those on the untreated surface. Also, the specific functions of human osteoblasts cultured on these media are enhanced on the treated alloy. In summary, laser peening tailors the Ti6Al4V surface to yield an oxidized layer with increased roughness that allows the colonization and activities of bone-lineage cells., This work was supported by grants PI12/01698 from Fondo de Investigaciones Sanitarias (FIS, Spanish Ministry of Economy and Competitiveness, MINECO, Spain), S2013/MIT-2862 from Comunidad de Madrid, MAT2009-14695-C04-01-02-04 from the former Spanish Ministry of Science and Innovation (MICINN), MAT2012-37736-C05-03-05 and MAT2014-52905- REDT (MINECO) and GR10149 (Junta de Extremadura, Spain). LC was the recipient of predoctoral fellowship BES-2010-034989 from MICINN. LS is supported by grant award CP11/00022 (FIS). NV is supported by Program I2 from Comunidad de Madrid (Spain).

© 2015 Elsevier Ltd. Roughening of Ti6Al4V by blasting with alumina or zirconia particles improves the mechanical fixation of implants by increasing the surface area available for bone/implant apposition. Additional thermal oxidation treatments of the blasted alloy have already shown to be a complementary low-cost solution to enhancing the in vitro biocompatibility and corrosion resistance of the alloy. In this work, the effects of oxidation treatment on a grit blasted Ti6Al4V biomedical alloy have been analysed in order to understand the net effect of the combined treatments on the alloy fatigue properties. Synchrotron radiation diffraction experiments have been performed to measure residual stresses before and after the treatments and microstructural and hardness changes have been determined. Although blasting of Ti6Al4V with small spherical zirconia particles increases the alloy fatigue resistance with respect to unblasted specimens, fatigue strength after oxidation decreases below the unblasted value, irrespective of the type of particle used for blasting. Moreover, at 700. °C the as-blasted compressive residual stresses (700. MPa) are not only fully relaxed but even moderate tensile residual stresses, of about 120. MPa, are found beneath the blasted surfaces. Contrary to expectations, a moderate increase in hardness occurs towards the blasted surface after oxidation treatments. This can be attributed to the fact that grit blasting modifies the crystallographic texture of the Ti6Al4V shifting it to a random texture, which affects the hardness values as shown by additional experiments on cold rolled samples. The results indicate that the oxidation treatment performed to improve biocompatibility and corrosion resistance of grit blasted Ti6Al4V should be carried out with caution since the alloy fatigue strength can be critically diminished below the value required for high load-bearing components., Financial support of MICINN (MAT2009-14695-C04) and MINECO(MAT 2012-37736-C05-01), Spain, is acknowledged. S. Barriuso thanks the JAEPre082-3 of CSIC-UE. The CIBER of Bioingeniería, Biomateriales y Nanomedicina is supported by the ISCIII.

This study addresses the roughening of AISI 316 LVM and Ti6Al4V by waterjet peening (WJP) without abrasive particles, looking for rough surfaces free of embedded particles that could act as severe notches. Strong parameters have been selected to characterize and check viability of abrasiveless WJP; a water pressure of 360. MPa and two slow traverse velocities: 0.05 and 0.1. m/min. After processing, large number of pits with undercuts plus some larger intrusions are observed, which are more abundant and larger in the steel specimens and in those treated with the lower traverse speed. Cross sectional examination of 316 LVM reveals a significant grain size refinement in the subsurface zone, 10-20. μm wide, that exhibits a submicrometric/nanometric grain size, accompanied with a hardness gradient (50% increase) that extends to a depth of up to about 100. μm. The analysis of the magnetic hysteresis loops discards the presence of strain induced α-martensite. No hardness or microstructural gradient was developed in the Ti6Al4V alloy. The results indicate that in AISI 316 LVM the volume loss occurs through hardening of the subsurface, embrittlement, crack formation and erosion. In Ti6Al4V the material removal may take place first at the vanadium reach β-phase. © 2011 Elsevier B.V.

Laser peening has recently emerged as a useful technique to overcome detrimental effects associated to another wellknown surface modification processes such as shot peening or grit blasting used in the biomedical field. It is worth to notice that besides the primary residual stress effect, thermally induced effects might also cause subtle surface and subsurface microstructural changes that might influence corrosion resistance. Moreover, since maximum loads use to occur at the surface, they could also play a critical role in the fatigue strength. In this work, plates of Ti-6Al-4V alloy of 7 mm in thickness were modified by laser peening without using a sacrificial outer layer. Irradiation by a Q-switched Nd-YAG laser (9.4 ns pulse length) working in fundamental harmonic at 2.8 J/pulse and with water as confining medium was used. Laser pulses with a 1.5 mm diameter at an equivalent overlapping density (EOD) of 5000 cm -2 were applied. Attempts to analyze the global induced effects after laser peening were addressed by using the contacting and non-contacting thermoelectric power (TEP) techniques. It was demonstrated that the thermoelectric method is entirely insensitive to surface topography while it is uniquely sensitive to subtle variations in thermoelectric properties, which are associated with the different material effects induced by different surface modification treatments. These results indicate that the stress-dependence of the thermoelectric power in metals produces sufficient contrast to detect and quantitatively characterize regions under compressive residual stress based on their thermoelectric power contrast with respect to the surrounding intact material. However, further research is needed to better separate residual stress effects from secondary material effects, especially in the case of low-conductivity engineering materials like titanium alloys.

© 2014 Elsevier B.V. Blasting of 316 LVM steel was performed by using alumina and zirconia particles that yield rough (up to Ra ~. 8. μm) and nearly smooth (up to Ra ~. 1. μm) surfaces, respectively. Besides roughening, the severe plastic deformation imposed during blasting yields subtle sub-surface microstructural changes such as grain size refinement, α'-martensite formation, and work hardening. In this work we investigate the thermal treatment at 700. °C of the blasted steel, aimed to reverse the strain induced α'-martensite to austenite, with special emphasis in the correlation of the microstructural changes with the fatigue resistance. Blasting with rounded zirconia particles increases the fatigue resistance whereas the opposite effect is observed using alumina ones, which are more abrasive and cause a huge amount of embedded particles acting as stress raisers. It is shown that thermal treatment at 700. °C is very effective in the reversion of martensite, even after 2. min of annealing. Interestingly, the short thermal treatment of the alumina blasted steel increases the fatigue strength to values close to non-blasted material (400. MPa). Prolonged exposures, however, contribute to a full relaxation of the beneficial compressive residual stresses, being the net effect a decrease in the fatigue limit (340. MPa)., The authors are thankful for financial support from the MICINN (MAT2009-14695-C04) and the MINECO (MAT 2012-37736-C05-01). S. Barriuso thanks to JAE predoc grant of CSIC. Technicians of Laboratories of X-Ray Diffraction, Mechanical Testing, and Microscopy (CENIM) and the SPM-Service of the ICMM-CSIC are specially acknowledged.

Grit blasting is used as a cost-effective method to increase the surface roughness of metallic biomaterials, as Ti. 6Al. 4V and 316 LVM, to enhance the osteointegration, fixation and stability of implants. Samples of these two alloys were blasted by using alumina and zirconia particles, yielding rough (up to Ra~8. μm) and nearly smooth (up to Ra~1. μm) surfaces, respectively. In this work, we investigate the sub-surface induced microstructural effects and its correlation with the mechanical properties, with special emphasis in the fatigue behavior. Blasting with zirconia particles increases the fatigue resistance whereas the opposite effect is observed using alumina ones. As in a conventional shot penning process, the use of rounded zirconia particles for blasting led to the development of residual compressive stresses at the surface layer, without zones of stress concentrators. Alumina particles are harder and have an angular shape, which confers a higher capability to abrade the surface, but also a high rate of breaking down on impact. The higher roughness and the presence of a high amount of embedded alumina particles make the blasted alloy prone to crack nucleation. Interestingly, the beneficial or detrimental role of blasting is more intense for the Ti. 6Al. 4V alloy than for the 316 steel. It is proposed that this behavior is related to their different strain hardening exponents and the higher mass fraction of particles contaminating the surface. The low value of this exponent for the Ti. 6Al. 4V alloy justifies the expected low sub-surface hardening during the severe plastic deformation, enhancing its capability to soft during cyclic loading. © 2013 Elsevier Ltd.

Grit blasting is a surface plastic deformation technique aimed to increase the surface area available for bone/implant apposition, which contributes to improve fixation and mechanical stability of Ti6Al4V implants. Besides roughening, grit blasting also causes surface contamination with embedded grit particles and subtle subsurface microstructural changes that, although does not challenge their biocompatibility, might influence other surface dominated properties like corrosion and ion release. Additional benefits are expected due to the induced compressive residual stresses, hence enhancing fatigue strength. The net effect depends on the type of particles used for blasting, but also on the amount of the subsurface cold work associated to the severe surface plastic deformation. In this work we study the potential of the non-contacting and contacting thermoelectric power (TEP) measurements in the analysis of the global changes induced in the Ti6Al4V when blasting the alloy with Al2O3 or ZrO2 particles, which yields a coarse and a fine rough surface, respectively. To reveal the effect of residual stresses, a set of specimens were thermally treated. The study proves that the non-contacting technique is more sensitive to the presence of residual stresses, whereas the contact technique is strongly influenced by the grain size refinements, work hardening and changes in solute, UMSNH (Mexico) and CENIM-CSIC (Spain) with a partial funding from CONACYT (Mexico) under project CB-80883 and MAT2009-14695-C04. The author H. Carreón wishes to thank CONACYT (Mexico) for the financial support during the sabbatical in CENIM-CSIC and S. Barriuso for the JAEPre082-3 of CSIC-UE

Grit blasting is a surface treatment process widely used to enhance mechanical fixation of the implants through increasing their roughness. Test samples of two metallic biomaterial alloys such 316LVM and Ti6Al4V were blasted by projecting Al2O3 and ZrO2 particles which yield a coarse and a fine rough surface. Then, the blasted samples were thermally treated before and after partial stress relaxation and measured by non-destructive thermoelectric techniques (NDTT), the non-contacting and contacting thermoelectric power (TEP) measurements respectively. It has been found that the TEP measurements are associated directly with the subtle material variations such as cold work and compressive residual stresses due to plastic deformation produced by grit blasting. The TEP measurements clearly demonstrate that the non-contact NDTT technique is very sensitive to the reverse transformation of the α'-martensite (blasted 316LVM) and the expected relaxation of compressive residual stresses with increasing the severity ...

Grit blasting is a low cost surface modification treatment widely used to enhance mechanical fixation of implants through increasing their roughness. As a result of the severe surface plastic deformation, beneath the surface it produces additional effects such as grain size refinement, work hardening and compressive residual stresses, which are generally evaluated with destructive techniques. In this research work, the blasting induced effects by Al2O3 and ZrO2 particles and their evolution after annealing at 700 °C were evaluated in 316LVM (Low Vacuum Melting) stainless steel specimens using two non-destructive thermoelectric techniques (NDTT), the non-contacting and contacting thermoelectric power measurements. Microstructural analysis and microhardness measurements performed beneath the blasted surface reveals that the non-contact NDTT results correlate well with the reversion of the α′-martensite developed during blasting, whereas the contact NDTT results are closely related to the grain size refinement and work hardening and the expected evolution of compressive residual stresses. Potential of these techniques to monitor subsurface changes in blasting processes and others severe surface plastic deformation techniques are clearly envisaged, This work was performed at UMSNH (Mexico) and CENIM-CSIC (Spain) with a partial funding from CONACYT (Mexico) under projects CB-80883 and MAT2009-14695-C04. H. Carreon wishes to thank CONACYT (Mexico) for the financial support during the sabbatical in CENIM-CSIC and S. Barriuso to CSIC for the JAE predoc.

Laser peening has recently emerged as a useful technique to overcome detrimental effects associated to another wellknown surface modification processes such as shot peening or grit blasting used in the biomedical field. It is worth to notice that besides the primary residual stress effect, thermally induced effects might also cause subtle surface and subsurface microstructural changes that might influence corrosion resistance. Moreover, since maximum loads use to occur at the surface, they could also play a critical role in the fatigue strength. In this work, plates of Ti-6Al-4V alloy of 7 mm in thickness were modified by laser peening without using a sacrificial outer layer. Irradiation by a Q-switched Nd-YAG laser (9.4 ns pulse length) working in fundamental harmonic at 2.8 J/pulse and with water as confining medium was used. Laser pulses with a 1.5 mm diameter at an equivalent overlapping density (EOD) of 5000 cm-2 were applied. Attempts to analyze the global induced effects after laser peening were addressed by using the contacting and non-contacting thermoelectric power (TEP) techniques. It was demonstrated that the thermoelectric method is entirely insensitive to surface topography while it is uniquely sensitive to subtle variations in thermoelectric properties, which are associated with the different material effects induced by different surface modification treatments. These results indicate that the stress-dependence of the thermoelectric power in metals produces sufficient contrast to detect and quantitatively characterize regions under compressive residual stress based on their thermoelectric power contrast with respect to the surrounding intact material. However, further research is needed to better separate residual stress effects from secondary material effects, especially in the case of low-conductivity engineering materials like titanium alloys., The authors acknowledge financial support from CONACYT (Mexico) under project CB-80883, MINECO (Spain), under projects MAT2009-14695-C04, MAT 2012- 37736-C05-01 and MAT 2012-37782

The grit blasting is a low-cost technique successfully used to enhance mechanical fixation of the implants through increasing their roughness. As a result of the severe plastic surface deformation, it produces subsurface effects such as grain refinement, hardening and compressive residual stresses which are generally evaluated with destructive techniques. In this research work, non-contacting and contacting thermoelectric power measurements are performed in blasted 316LVM and Ti-6Al-4V specimens using Al2O3 and ZrO2 particles which yield a coarse and a fine rough surface, respectively. This study correlates the microstructural changes induced by the grit blasting treatment and the limitations and advantages of each of the nondestructive thermoelectric techniques based on the Seebeck effect used to evaluate these biomaterials.