It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Deep rolling (DR) is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of DR on the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) behavior of a Ti–6Al–4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near-surface microstructures. Preliminary results on laser shock peened Ti–6Al–4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ∼450 °C, i.e. at a homologous temperature of ∼0.4 T/T m (where T m is the melting temperature). Based on cyclic deformation and stress/life ( S / N ) fatigue behavior, together with the X-ray diffraction and in situ transmission electron microscopy (TEM) observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti–6Al–4V at such higher temperatures, despite the almost complete relaxation of the near-surface residual stresses. In the absence of such stresses, it is shown that the near-surface microstructures, which in Ti–6Al–4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment.

On the influence of mechanical surface treatments—deep rolling and laser shock peening—on the fatigue behavior of Ti–6Al–4V at ambient and elevated temperatures

Grain refinement mechanism of multiple laser shock processing impacts on ANSI 304 stainless steel

Grain refinement of LY2 aluminum alloy induced by ultra-high plastic strain during multiple laser shock processing impacts

Laser peening without protective coating (LPPC) has been applied to water-immersed SUS304 (Type 304) and SUS316L (Type 316L) austenitic stainless steels. The surface residual stress of both materials was converted from tensile to compressive of several hundreds of megapascals by LPPC with a Q-switched and frequency-doubled Nd:YAG laser. The depth of the compressive residual stresses after LPPC exceeded 1 mm from the surface. Accelerating stress corrosion cracking (SCC) tests in a high-temperature and corrosive-water environment showed that LPPC completely prevented the SCC initiation of sensitized SUS304. SCC tests of pre-cracked samples were also performed for SUS304, which indicated that LPPC inhibits the propagation of the small pre-cracks. Rotating bending tests demonstrated that the fatigue strength of SUS316L with LPPC is enhanced by 1.4–1.7 times compared to that of the reference material at 108 cycles.

Retardation of crack initiation and growth in austenitic stainless steels by laser peening without protective coating

The laser shock peening (LSP) process using a Q-switched pulsed laser beam for surface modification has been reviewed. The development of the LSP technique and its numerous advantages over the conventional shot peening (SP) such as better surface finish, higher depths of residual stress and uniform distribution of intensity were discussed. Similar comparison with ultrasonic impact peening (UIP)/ultrasonic shot peening (USP) was incorporated, when possible. The generation of shock waves, processing parameters, and characterization of LSP treated specimens were described. Special attention was given to the influence of LSP process parameters on residual stress profiles, material properties and structures. Based on the studies so far, more fundamental understanding is still needed when selecting optimized LSP processing parameters and substrate conditions. A summary of the parametric studies of LSP on different materials has been presented. Furthermore, enhancements in the surface micro and nanohardness, elastic modulus, tensile yield strength and refinement of microstructure which translates to increased fatigue life, fretting fatigue life, stress corrosion cracking (SCC) and corrosion resistance were addressed. However, research gaps related to the inconsistencies in the literature were identified. Current status, developments and challenges of the LSP technique were discussed.

/pdf/laser-peening-process-and-its-impact-on-materials-properties-1up080uvlh.pdf

Laser Peening Process and Its Impact on Materials Properties in Comparison with Shot Peening and Ultrasonic Impact Peening

Laser shock processing and its effects on microstructure and properties of metal alloys: a review

Synthesis of yttrium titanate stannate (Y
 2
 Ti
 2‐
 
 x
 
 Sn
 
 x
 
 O
 7
 ,

LnUO
 4
 based glass‐ceramic composites as waste forms for the immobilization of lanthanide‐bearing uranium wastes

We report a flux crystal growth of Ba2[(UO2)2Ti2O8] and subsequent structural and spectroscopic studies using multiple techniques. The layered crystal structure, built up with sheets of edge-sharing dimeric uranyl pentagonal bipyramids and dimeric TiO5 square pyramids with interlayer Ba(II) ions, was revealed by synchrotron single crystal x-ray diffraction and confirmed with electron diffraction using a transmission electron microscope. The presence of only hexavalent uranium was confirmed by both diffuse reflectance and x-ray absorption near-edge structure spectroscopies, consistent with the bond valence sum calculations. Its vibrational modes were revealed by Raman spectroscopy. In addition, its implications as a potential hexavalent uranium waste form for the immobilization of uranium-rich radioactive wastes were discussed. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/jace.18792

Flux crystal growth of Ba
 2
 [(UO
 2
 )
 2
 Ti
 2
 O
 8
 ]: structures, spectroscopies and implications

Two synthetic uranium oxide hydrates with Ba(ii) ions, a 2D layered structure and a complex 3D structure, were synthesised hydrothermally and characterised.

/pdf/investigation-of-uranium-oxide-hydrates-with-barium-ii-ions-1gqsg7xa.pdf

Tao Wei

Papers

Laser shock processing and its effects on microstructure and properties of metal alloys: a review

Synthesis of yttrium titanate stannate (Y <sub>2</sub> Ti <sub>2‐</sub> <i> <sub>x</sub> </i> Sn <i> <sub>x</sub> </i> O <sub>7</sub> ,

LnUO 4 based glass‐ceramic composites as waste forms for the immobilization of lanthanide‐bearing uranium wastes

Flux crystal growth of Ba <sub>2</sub> [(UO <sub>2</sub> ) <sub>2</sub> Ti <sub>2</sub> O <sub>8</sub> ]: structures, spectroscopies and implications

Investigation of uranium oxide hydrates with barium(ii) ions: structural diversity, uranium valences and implications