A Through-Process Experimental Approach to Enable Optimization of Cold Sprayed Al 7075 Consolidation Performance

This work employs an example of a through process experiment systematic approach to study the relationship among powder properties, cold spray (CS) processing parameters, and consolidated specimen behavior through a combined effort of characterization methods and computational models. This process will allow for the systematic isolation of variables that can affect powder and CS deposit properties. In this study, Al 7075 powder was used as feedstock to produce a CS coating using industry-standard processing parameters. Techniques such as SEM, EDS, XRD, nanoindentation, and tensile testing were used to characterize the properties of both the feedstock powder and CS deposits. In addition, computational thermodynamic modeling was used to guide the interpretation of microstructural features of the powder and CS specimen. Finally, an additive yield strength model was employed to quantify the strengthening components introduced through the CS process.

Characterization of Spatter and Sublimation in Alloy 718 during Electron Beam Melting

Due to elevated temperatures and high vacuum levels in electron beam melting (EBM), spatter formation and accumulation in the feedstock powder, and sublimation of alloying elements from the base feedstock powder can affect the feedstock powder’s reusability and change the alloy composition of fabricated parts. This study focused on the experimental and thermodynamic analysis of spatter particles generated in EBM, and analyzed sublimating alloying elements from Alloy 718 during EBM. Heat shields obtained after processing Alloy 718 in an Arcam A2X plus machine were analyzed to evaluate the spatters and metal condensate. Comprehensive morphological, microstructural, and chemical analyses were performed using scanning electron microscopy (SEM), focused ion beam (FIB), and energy dispersive spectroscopy (EDS). The morphological analysis showed that the area coverage of heat shields by spatter increased from top (<1%) to bottom (>25%), indicating that the spatter particles had projectile trajectories. Similarly, the metal condensate had a higher thickness of ~50 μm toward the bottom of the heat shield, indicating more significant condensation of metal vapors at the bottom. Microstructural analysis of spatters highlighted that the surfaces of spatter particles sampled from the heat shields were also covered with condensate, and the thickness of the deposited condensate depended on the time of landing of spatter particles on the heat shield during the build. The chemical analysis showed that the spatter particles had 17-fold higher oxygen content than virgin powder used in the build. Analysis of the metalized layer indicated that it was formed by oxidized metal condensate and was significantly enriched with Cr due to its higher vapor pressure under EBM conditions.

Detonation Spraying of Hydroxyapatite on a Titanium Alloy Implant

Hydroxyapatite (HA), the major mineral component of tooth enamel and natural bones, is a good candidate for bone tissue engineering. Synthetic HA is used for making coatings on metallic implants intended for medical applications. A HA coating renders the implant biocompatible and osteoinductive. In addition, it improves fixation and the overall performance of the implanted object. In the present work, HA coatings were deposited on a medical titanium alloy implant with mesh geometry and a developed surface by detonation spraying. The feedstock powder was HA obtained by the dry mechanochemical method. Single-phase HA coatings were obtained. The coatings were formed not only on the surfaces normal to the particle flow direction, but also on the sides of the mesh elements. Despite partial melting of the powder, no decomposition of HA occurred. This work demonstrates the prospects of detonation spraying for the production of HA coatings on metallic implants with complex geometries.

Synthesis and Pressure-Assisted Sintering of CaCu3Ti4O12 Dielectrics

In this paper, we examined the dielectric properties of CaCu3Ti4O12 (CCTO) ceramics fabricated by various routes and discussed the most important conditions affecting their dielectric behavior. We prepared feedstock powder using a molten salt route and compared it with a commercial powder. Both powders were sintered using SPS. For some samples, annealing was applied after sintering. Other samples were obtained by high-pressure forming and conventional sintering, using both powders. Phase composition, porosity and microhardness were evaluated in comparison with the literature. The results showed that a sintering temperature just below or equal to 1000 °C should be set for the SPS process. However, the best dielectric characteristics were obtained in samples prepared by high-pressure forming and conventional sintering, which showed a relative permittivity of 22,000 and a loss tangent of 0.13 at 1 MHz.

High Temperature Sliding of TiC Based Hardmetal Coatings Against TWIP Steel

Manufacturing of steel components is often done at high temperatures (HT) posing a serious challenge to components such as forming tools. Thermal spray coatings provide a cost-effective solution for surface protection under HT, corrosive environments and severe wear conditions. Thermally sprayed coatings based on cubic hard materials such as TiC and TiCN can provide an alternative to widely used Cr3C2-NiCr. While the latter possess a superb oxidation resistance and wear resistance at HT, they are prone to degradation in the presence of Mn, an element commonly alloyed in many modern steel grades such as TWIP (twinning-induced plasticity steel). In this study, a (Ti,Mo)(C,N)-29% Ni hardmetal feedstock powder was prepared by agglomeration and sintering. Coatings were deposited using a high velocity air-fuel (HVAF) spray process. The coating was benchmarked against a standard Cr3C2-NiCr coating obtained with the same spray process. Our work comprises analyses of the feedstock powder along with the resulting coating microstructure after deposition and heat treatment. Further, the HT sliding behavior against TWIP steel using a HT pin-on-disc tribometer at 700°C was investigated. The results showed a clear benefit of the TiCN-based coating, with almost no wear detected, while the Cr3C2-coating showed a significant wear loss. Based on these results, the TiCN-based coating is regarded as potential solution for prospective forming applications of modern high Mn steels, such as TWIP.

The Cavitation Resistance of WC-10Co4Cr and WC-20CrC-7Ni HVAF Coatings

Two kinds of cermet powders, WC-10Co4Cr and WC-20CrC-7Ni, were deposited on 1040 steel via high velocity air fuel (HVAF) spraying to evaluate resistance in cavitation erosion conditions with additional electrochemical effects. Coating microstructure, phase composition, and microhardness were examined along with the topography of eroded surface layers. The cavitation resistance of the WC-20CrC-7Ni coating was found to be approximately 1.3 times greater than that of the other coating, which can be attributed to its finer grain structure, lower pore density, and the presence of high Cr and Ni content in the feedstock powder which serves to strengthen the matrix.

The Coatings Formation and Characteristic of a Low Pressure Thermal Plasma Torch

Compared with the atmosphere plasma spraying (APS), low pressure plasma spraying (LPPS) has been widely used due to deposit a specific and unique coating. A new low pressure thermal spraying plasma torch was designed according to the plasma spray characteristic in the low pressure environment. The plasma jet characteristic and the coatings microstructure were analyzed. In this study, Kundsen number has a great effect on the heat transfer of feedstock powder. With the increase of current, the plasma torch efficiency will decrease. A equiaxed microstructure of 316L coatings were deposited.