Laser Beam Welding of a Low Density Refractory High Entropy Alloy

The effect of laser beam welding on the structure and properties of a Ti1.89NbCrV0.56 refractory high entropy alloy was studied. In particular, the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam welding at room temperature resulted in the formations of hot cracks. Sound butt joints without cracks were produced using pre-heating to T ≥ 600 °C. In the initial as-cast condition, the alloy consisted of coarse bcc grains with a small amount of lens-shaped C15 Laves phase particles. A columnar microstructure was formed in the welds; the thickness of the grains increased with the temperature of pre-heating before welding. The Laves phase particles were formed in the seams after welding at 600 °C or 800 °C, however, these particles were not observed after welding at room temperature or at 400 °C. Soaking at elevated temperatures did not change the microstructure of the base material considerably, however, “additional” small Laves particles formed at 600 °C or 800 °C. Tensile test of welded specimens performed at 750 °C resulted in the fracture of the base material because of the higher hardness of the welds. The latter can be associated with the bcc grains refinement in the seams.

Microstructure and Properties of Q345E Lamellar Tearing Resistant Steel SAW Welding Joints

The Q345E lamellar tearing resistant steel with 140mm thickness was welded by submerged arc welding (SAW). The microstructure and properties of the welded joints were investigated. Affected by the long-term welding thermal cycle, microstructure at different thickness has great differences. The hardness in the weld center is higher about 55 HV than the base metal. Due to the grains refinement of the microstructure at 1/2 thickness was more obvious, the microhardness of this zone has a more obvious dispersion degree. The average grain size of ferrite at the 1/4 thickness is about 10 μm, which resulted in two samples at this thickness obtain a higher tensile strength (496.568 MPa and 496.36 MPa). Moreover, part of the pearlite lamellar in the HAZ at 1/4 thickness had been fragmented and spheroidized.

Investigation on Work Hardening Effect Generated during Dynamic Formation of Al-Based Coating on Magnesium Alloy

Numerical simulation of sequential collision behavior of multi-particles during dynamic formation of Al-based coating on magnesium alloy by supersonic particles deposition demonstrated that continuous tamping effect from subsequent sprayed particles improved significantly compression ratio of former deposited particle and promote effectively deformation and spread out. Analysis to morphology and microstructure of Al-based coating on magnesium alloy by SEM and TEM elicited that subsequent sprayed particles generated two effects including erosion and compaction to former deposited layer of the coating, induced formation of high density dislocation, grains refinement and re-crystallization, which played work-hardening strengthening effect and fine crystal strengthening effect to Al-Si coating.

Effects of MgO and Y2O3 on the Microstructure and Mechanical Properties of Al2O3 Ceramics

Al2O3-MgO, Al2O3-Y2O3 and Al2O3-MgO-Y2O3 composite ceramics were fabricated respectively by hot-press sintering technique. With the analysis of the mechanical properties and microstructure, it was found that single additive MgO could be more favorable to the grains’ refinement and densification than Y2O3; the composite additive including both MgO and Y2O3 was better than single additive MgO or Y2O3, because their interactions could improve the mechanical properties of the Al2O3 ceramics; The sintering temperature could be reduced by adding the suitable amount of composite additives.

The Effect on the Surface of Ti-5Al-2Sn-2Zr-4Mo-4Cr by Laser Shock Peening

Under the terrible environment in the aero-engine, the blade, made of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy, is prone to result in fatigue failure. So improving the titanium alloy performance is becoming very significant. In this paper, the microstructure and microhardness of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy with and without laser shock peening (LSP) were examined and compared by XRD, TEM and microhardness test. The XRD tests pointed out that LSP generated the microstrains and grains refinement in the material surface. The TEM results indicated that great high density dislocations were generated and evolved into the dislocation wall, small-angle boundary and large-angle boundary. The nanocrystallites were formed and became more and more uniform after 4GW/cm2. The grains nanocrystallization in the surface layer helps to improve the material performance. The microhardness test result showed that LSP could increase the hardness by 20 percent or so. And the affected depth is about 700μm.

Effect of Sandblasting and Surface Mechanical Attrition Treatment on Surface Roughness, Wettability, and Microhardness Distribution of AISI 316L

Surface roughness and wettability determines the stability of bone-implant integration. Stable implants can be found in those with a rough and hydrophilic surface. Sandblasting and surface mechanical attrition treatment (SMAT) are among the current techniques to obtain surface with such typical properties. In addition, both treatments increase mechanical strength of metal through surface grains refinement. In this paper, the effect of sandblasting and SMAT on surface roughness, wettability, and microhardness distribution of AISI 316L is discussed. All treatments were conducted for 0-20 minutes. The result shows a rougher and a more hydrophilic surface on the sandblasted samples rather than on those with SMAT. A harder surface is yielded by both treatments, but the SMAT produces a thicker hardened layer.

Fracture Failure Analysis of Twin Rolling Casting Magnesium by Hot Compression

The flow stresses of AZ41M and ZK 60 wrought magnesium alloys under the deformation conditions of twin rolling casting and hot compression (TRC-HC) at different temperature and strain rates were studied. The deformation behavior and failure mechanism of them were discussed. The microstructure evolutions were analyzed by OM and EBSD technique. The results indicated that AZ41M and ZK 60 have different strain-stress curve under the same conditions. Working hardening results in occurrence of cracks in or around the shear bands. The recrystallized, equiaxed and fined grains in shear bands attribute to recovery and recrystallization, grains refinement causes local working hardening as well as decreases of crack tip driving forces. The stresses concentrate in shear bands causing cracks initiation and propagation. Casting defects to be the nucleus of cracks is another failure mode. With the increases of strains, dislocations rearrange forming sub-grains, the low angle grain boundaries (LAGBs) continuously evolved into high angle grain boundaries (HAGBs).

Grain refinement effect of pulsed magnetic field on solidified microstructure of superalloy IN718

The refinement mechanism of pulsed magnetic field (PMF) was discussed by experimental investigation, and the effects of exciting frequency, exciting voltage, and delay time of PMF on grains refinement of superalloy were studied. The experimental results show that, as exciting frequency or exciting voltage is increased, the grains are refined. However, the grains become coarse when frequency increases further. As delay time of PMF increases, the grain size increases. The refinement effect of PMF is attributed to the detachment of heterogeneous nuclei on the mold wall and subsequently separation of nuclei in the melt. The Joule heat can prolong the continuous nucleation process. However, the refinement effect will be impaired if the Joule heat is strong enough to remelt the detached nuclei.

Rosenhain Centenary Conference - 3. Materials development present and future 3.2 Controlled rolling

Controlled rolling is a means whereby the properties of steel can be improved to a level equivalent to those of more highly alloyed or heat-treated steels. The processing conditions are controlled to refine the austenite structure and thereby give fine ferrite grains. Refinement of the structure is aided by the addition of micro-alloying elements such as Nb, V or Ti. The improved strength and toughness of controlled rolled steels are shown to be a result of the fine grain size. A further increase in strength beyond that due to grain refinement can be obtained by finishing rolling at low temperatures in the y + oc or cc regions. Commercial controlled rolling in various mill layouts, together with some properties obtained are described and it is pointed out that optimization of productivity is a major consideration when controlled-rollmg procedures are being planned.