A combined heat source model for the prediction of residual stress post extreme high-speed laser material deposition

The preparation of Ti coatings on mild steel can both effectively improve the corrosion resistance of the substrate and reduce the application cost of Ti, which is an effective measure to improve the service performance of mild steel in the marine environment. Plasma cladding technology is an efficient method for preparing metal coatings, and the type of powder is a key process parameter for coating preparation. In this work, high-performance Ti coatings are prepared on the surface of mild steel by plasma cladding technology, and the effects of different particle sizes and shapes of Ti powders on the surface morphology, microstructure and properties of the coatings are studied. The results show that powder particle size and sphericity are the key factors affecting the morphology, structure and service performance of Ti coatings. After 1000 h of salt spray test, the spherical powder cladding coatings only suffer slight corrosion, while the irregular shape powder coating is more severely corroded. Powder cladding with moderate powder particle size and good sphericity have a smoother coating and fewer defects. Ti powders with different particle sizes and shapes all have the diffusion of Fe element during the cladding process. The surface of Ti coating prepared by spherical powder are dominated by α-Ti and Fe0.2Ti0.8 phases, while the surface of Ti coating prepared by irregular shape powder is dominated by FeTi and Ti2Fe. The interface between the coating and the substrate shows metallurgical bonding, and the increase in Ti-Fe brittle phase will deteriorate the mechanical properties and corrosion resistance of the coating. The shear strength of coatings prepared from spherical Ti powders of 75–150 μm can reach 105.18 MPa, the corrosion potential is the most positive (−0.2206 V), and the self-corrosion current density is the lowest (6.220 × 10−8 A/cm2).

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Effect of Powder Particle Size and Shape on Appearance and Performance of Titanium Coatings Prepared on Mild Steel by Plasma Cladding

The extremely severe conditions at which cutting tools are exposed in hard machining operations require tool materials with outstanding mechanical properties. Excellent combinations of high hardness and fracture toughness are aimed to enhance wear and contact damage resistance; and thus, reliability of the tool. Here, spherical indentation is used to induce controlled damage, under monotonic loads, and to assess the resulting damage scenario of polycrystalline cubic boron nitride (PcBN). In doing so, two grades with different content of cBN particles as well as chemical nature of the binder are investigated. Systematic and detailed inspection of residual imprints, by means of optical and scanning electron microscopy, is conducted to document critical loads for damage emergence and evolution through different stages, as a function of increasing load and microstructural assemblage. It is found that H-PcBN grade, with higher content of cBN particles and a metallic binder, exhibits higher resistance to crack nucleation as well as a more gradual transition between distinct damage scenarios. This enhanced response is linked to the concomitant increase of hardness and fracture toughness observed for that grade, as compared to the L-PcBN one, consisting of a significantly lower amount of superhard particles bound by a binder of ceramic nature. In-depth inspection of interaction between fissures and microstructure indicates the existence of four different crack paths for both PcBN grades - transgranular through cBN particles, across the binder phase, and intergranular along either cBN/cBN or cBN/binder interfaces. Relative frequency of these crack paths as well as operative toughening mechanisms define the effective crack growth resistance of each PcBN grade. In this regard, a higher fracture toughness is assessed for H-PcBN, as a result of crack bridging by metallic ductile ligaments together with the effective barrier-like role played by substructural features within cBN particles. Meanwhile, L-PcBN grade shows a rather low crack growth resistance, in direct correlation with the intrinsic brittle nature of the contiguous ceramic binder through which crack extension predominantly takes place. These relative differences in resistance to crack nucleation and growth become key for understanding the enhanced contact damage behaviour determined for the grade with higher content of cBN particles in this study. 

Spherical indentation of polycrystalline cubic boron nitride (PcBN): Contact damage evolution with increasing load and microstructural effects

2D Ultrasonic-Assisted Burnishing to Control Surface Integrity and Electrochemical Behavior of AA7075-T6 Aluminum Alloys

ABSTRACT The burnishing process was performed using different feed rates, rotational speed and penetration depth parameters to alloy Al 7175-T6. Surface roughness, fatigue life and hardness of the samples were determined. Microstructural examinations of the samples were performed. In the surface roughness measurements, occurred a linear increase in proportion to the increasing feed rate. The increase in the penetration depth affected negatively the surface roughness. Significant increases were acquired in the fatigue life of the burnished samples. The hardness values of the burnishing samples are higher than the hardness value of the base material. The rotational movement of the steel ball during the burnishing process were been caused the aspect ratio of the grains in the microstructure to change.

Effect of ball-burnishing on surface integrity and fatigue behaviour of 7175-T6 AA

Characterization of microstructure and mechanical properties for Ti-6Al-4 V processed by rotary ultrasonic roller burnishing

The wear behavior of a single-layer electroplated cubic boron nitride (cBN) grinding wheel was investigated in creep feed grinding Inconel 718 narrow-deep-groove with a width of 2 mm. In this paper, the protrusion height of cBN grits on the side edge of the grinding wheel was measured by three-dimensional optical profiler, and a scanning electron microscope was used to detect the topography of worn cBN grit and the nickel bonding layer. The investigation results indicated that the steady wear stage of the grinding wheel shared more than 84.6% of the wheel life span, and the machining precision of the grinding wheel was kept at a high level. The fracture mode of the cBN grit was proven to be cleavage. The sources of the cleavage cracks were observed on the surface of wear flat or the side surface of the cBN grit. The holding strength of cBN grit could be weakened due to the joint surface breakage, the displacement of grit, or the cracks of the nickel bonding layer. The transition layer was contributed to the decrease of the bonding strength. Severe macro fractures and the concentration of pulled out grits were observed on the transition edge and the inner area of the side edge, separately. This study provides a deep understanding of the wear mechanism of a single-layer electroplated cBN grinding wheel.

Investigation of the wear behavior of abrasive grits in a dry machining Inconel 718 narrow-deep-groove with a single-layer cubic boron nitride grinding wheel

Improving the wear resistance and corrosion resistance of high-speed steel (HSS), WC/diamond/Co-based gradient composite coatings were produced on HSS substrates by laser cladding with different composition powder mixture (Co-Cr alloy powder, 80Co-Cr alloy powder+20WC, 53Co-Cr alloy powder+40WC+7diamond, wt%). The macromorphology, microstructures, and phase composition were characterized by optical microscope (OM), scanning electron microscopy (SEM) equipped with energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD) techniques. The microhardness, wear resistance, and corrosion resistance of the gradient coatings were also investigated, respectively. The results indicate that the prepared WC/diamond/Co-based gradient composite cladding layer has a fine morphology on the cross sections and a gradient transition of the grain size has been achieved. The microhardness result presents gradient distribution along the depth of the coating. The microhardness is strengthened due to the dispersions of M7C3 (M is Fe, Cr), Co3C, CrCo, Cr3C2, and Fe3C in the composite coating, and the highest microhardness of 1342 HV0.2 can be detected in the cladding layer. The friction coefficient values of the coatings range from 0.27 to 0.40, which is much lower than that of the substrate (0.50–0.60). Furthermore, the wear loss of coatings (1.1 mg) decreases by more than 3 times comparing with that of the substrate (3.5 mg). The polarization resistance results show that the cladding layer has excellent corrosion resistance with polarization resistance that can reach the value of 236488.1 Ω·cm2. The gradient transition of the mechanical properties and chemical metallurgical combination between particle (WC, diamond) and adhesive phase can be obtained in laser cladding, which improves the wear resistance and corrosion resistance of the HSS surface.

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Microstructure and Properties of WC/diamond/Co-based Gradient Composite Coatings on High-speed Steel Fabricated by Laser Cladding

The invention relates to the technical field of casting manufacturing and cooling, in particular to a quantitative control atomization cooling device. The device solves the technical problems in the background art. The device comprises a liquid conveying pipeline, a gas conveying pipeline, a cooling liquid quantitative control unit, a gas quantitative control unit, a stepped Venturi tube, a conical Venturi tube, an atomizing chamber, two sets of joint hoses, a spray head and a closed box body. According to the device, cooling liquid and compressed gas can be quantitatively controlled through the cooling liquid quantitative control unit and the gas quantitative control unit respectively; the cooling liquid is automatically sucked into the pipeline through the negative pressure effect generated through the stepped Venturi tube and the conical Venturi tube, and meanwhile airflow disturbance can be increased, so that an atomized flow is more uniform and sufficient; a disturbance airflow generated through the two sets of joint hoses can prevent the atomized flow from forming hydrops in the transmission process, the two sets of joint hoses can be flexibly bent and are suitable for cooling complex workpieces in different environments; and the atomizing effect is good, and the casting blank quality is guaranteed.

Xinhui Hao

Papers

Characterization of microstructure and mechanical properties for Ti-6Al-4 V processed by rotary ultrasonic roller burnishing

Investigation of the wear behavior of abrasive grits in a dry machining Inconel 718 narrow-deep-groove with a single-layer cubic boron nitride grinding wheel

Microstructure and Properties of WC/diamond/Co-based Gradient Composite Coatings on High-speed Steel Fabricated by Laser Cladding

Quantitative control atomization cooling device