Microstructure and high temperature oxidation resistance of Si-Y co-deposition coatings prepared on TiAl alloy by pack cementation process

In order to improve the high temperature oxidation resistance of TiAl alloy, Y modified silicide coatings were prepared by pack cementation process at 1030, 1080 and 1130 °C, respectively, for 5 h. The microstructures, phase constitutions and oxidation behavior of these coatings were studied. The results show that the coating prepared by co-depositing Si?Y at 1080 °C for 5 h has a multiple layer structure: a superficial zone consisting of Al-rich (Ti,Nb)5Si4 and (Ti,Nb)5Si3, an out layer consisting of (Ti,Nb)Si2, a middle layer consisting of (Ti,Nb)5Si4 and (Ti,Nb)5Si3, and aγ-TiAl inner layer. Co-deposition temperature imposes strong influences on the coating structure. The coating prepared by Si?Y co-depositing at 1080 °C for 5 h shows relatively good oxidation resistance at 1000 °C in air, and the oxidation rate constant of the coating is about two orders of magnitude lower than that of the bare TiAl alloy.

Si-Al-Y Co-deposition Coatings Prepared on Ti-Al Alloy for Enhanced High Temperature Oxidation Resistance

Si-Al-Y co-deposition coatings were prepared on Ti-Al alloy by pack cementation processes at 1 050 ℃ for 4 h with different halide activators in the packs for enhancing the high temperature oxidation resistance of Ti-Al alloy. The structure, constituent phases, formation process and oxidation behavior of the coatings were investigated. The experimental results showed that the coatings prepared respectively with NaF and NH_4Cl as activators were composed of a（Ti, X）_5Si_4,（Ti, X）_5Si_3（X represents Nb and Cr）, and TiSi_2 outer layer, a TiAl_2 inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi_2 in the outer layer and（Ti, X）_5Si_4 and（Ti, X）_5Si_3 phases were observed in the middle layer of the coating prepared with AlCl_3·6H_2O activator. Among the halide activators studied, the coating prepared with AlCl_3·6H_2O was thicker and denser, which is the only suitable activator for pack Si-Al-Y co-deposition coatings on a Ti-Al alloy. The oxidation results show that the coating can protect the Ti-Al alloy from oxidation at 1000 ℃ in air for at least 80 h. The excellent oxidation resistance of the coating is attributed to the formation of a dense scale mainly consisted of TiO_2, SiO_2 and Al_2O_3.

Experimental study on the microstructural and anti-corrosion behaviour of Co-deposition Ni-Co-SiO_2 composite coating on mild steel

Mild steel is commonly used in the construction of Pipeline. The major problem of this Pipeline is corrosion. Effort is make my researchers to combat this problem. In this work Co-deposition of Ni-CoSiO_2 composite coating on mild steel was reported with the view to reduce this problem. The SiO_2 was varies from 5 to 25 wt% in the deposition. The microstructure, hardness values and potentiodynamic polarization in simulated sea water were determined. The results show that XRD pattern of the Ni Co deposited mild steel revealed the presence hard phases of NiO, Co_5Ni, Co_2Ni_3, Ni Co5 while that of Ni-CoSiO_2 deposited mild steel revealed the presence harder phases of NiOSiO_2, CoNi_7Si_2, Co_5Ni_2Si_3. The NiCo-25 SiO_2 deposited sample has smaller particle size than Ni-10 Co coating. Coating thickness of 110.7 mm was obtained for Ni-10 Co coating, while coating thickness of 135.7, 157.7, 165.0 mm were obtained at Ni-10 Co-x SiO_2(x=10, 15, 25 wt%). 99.90% corrosion resistance was achieved at Ni-Co-25 SiO_2. This improvement in corrosion resistance after composites coating could be attributed to the hard and fine structure obtained after coating.

Processing and oxidation of co-deposited Ni-Al coatings

Electrodeposited Ni matrix/Al microparticles or nanoparticles dispersed composite coatings (termed as EMCCs or ENCCs) are developed from a Ni-based electrolyte bath. The Al microparticles are in a size range of 1 -5 μm and the Al nanoparticles in an average size of 75 nm. The Al content in coatings increases with increase in the particle content in the bath. Particle size effect on the degree of codeposition is not significant. However, codeposition of Al nanoparticles instead of microparticles promotes more homogenous growth of Ni deposits on {111}, {200} and {220} planes. The oxidation at 1 050 ℃ of the as-deposited composite coatings shows that at a comparable Al content, ENCC of Ni-Al exhibits a better oxidation resistance than EMCC of Ni-Al due to the fast formation of an alumina scale during the transient stage of oxidation.

Effects of submicron diamonds on the growth of copper in Cu-diamond co-deposition

Submicron diamonds were co-deposited on aluminum substrates with copper from the acid copper sulfate electrolyte by electro- lyte-suspension co-deposition. After submicron diamonds were added to the electrolyte, the shape of copper grains transformed from oval or round to polyhedron, the growth mode of copper grains transformed from columnar growth to gradual change in size, and the preferred ori- entation of copper grains transformed from （220） to （200）. Analyzing the variation of cathodic overpotential, it was found that the cathodic overpotential tended to remain tmchanged when copper plane （220） grew in the process of electrodepositing pure copper, while it tended to decrease with time when copper plane （200） grew in the process of co-deposition. It was inferred that copper plane （200） was propitious to the deposition of submicron diamonds.

Si-Al COATING ON PURE MOLYBDENUM SUBSTRATE AND ITS CYCLIC OXIDATION BEHAVIOR

The halide-activated pack cementation method is utilized to codeposit aluminum and silicon on Mo substrate. Emphasis is placed on the microstructure and elevated-temperature oxidation resistance of coatings. The results show that hexagonal Mo(Si, Al)2 as a main phase and a little amount of the lower disilicide Mo5Si3 was formed on Mo substrate through the halide-activated pack cementation method. The resultant Si-Al coating on Mo substrate exhibits excellent cyclic oxidation resistance. The excellent cyclic oxidation resistance of the coatings is attributed to the formation of alumina on the coatings during the oxidation.

Preparation of ZrC-SiC composite coatings by chemical vapor deposition and study of co-deposition mechanism

In this work, the Zr C-SiC composite coatings were co-deposited by chemical vapor deposition(CVD)using ZrCl4, MTS, CH4 and H2 as raw materials. The morphologies, compositions and phases of the composite coatings were characterized by scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS) and X-ray diffraction(XRD). The results indicated that the morphologies, compositions and phases of the composite coatings were related to the deposition temperature, the flow rate of the carrier H2 gas, and the ratio of C/Zr. Moreover, the co-deposition mechanism of the composite coatings was also studied. It was found that different deposition temperatures resulted in different deposition mechanisms. At temperatures in the range of 1150–1250℃, the Zr C-SiC co-deposition was controlled by the surface kinetic process. At temperatures in the range of 1250–1400℃, the Zr C-SiC co-deposition was controlled by the mass transport process.

Effects of Y_2O_3/Y on Si-B co-deposition coating prepared through HAPC method on pure molybdenum

In order to clarify the effects of reactive element Y on the properties of Si-B co-deposition coating on Mo substrate, the Si-B-Y2O3 and Si-B-Y co-deposition coatings were prepared at 1300 ℃ for 5 h by using the pack mixtures 16Si-4B-xY2O3/Y- 4NaF-（76–x）Al2O3 （wt.%,x=0, 0.5, 1, 2, 4, 8）. X-ray diffraction （XRD）, energy dispersive spectroscopy （EDS） and wavelength dis-persive spectroscopy （WDS） techniques were used to analyze the structure and oxidation behavior of these coatings. The results re-vealed that the Si-B-Y2O3 and Si-B-Y co-deposition coatings had the same structure with that of the Si-B co-deposition coating. However, Y was incorporated into these coatings and the thicknesses of these coatings were thicker than that of the Si-B co-deposition coating. In addition, the Si-B-Y co-deposition coating demonstrated better cyclic oxidation resistance than the Si-B co-deposition coating at 1100 ℃. The modifying mechanism of Y on the Si-B co-deposition coating was discussed.

TiAlN/Cu Nanocomposite Coatings Deposited by Filtered Cathodic Arc Ion Plating

TiAIN]Cu nanocomposite coatings with Cu concentration of 0-1.4 at.% were deposited on the high- speed steel （HSS） substrates by filtered cathodic arc ion plating technique. The chemical composition, microstructure, morphology, adhesion strength, mechanical and tribological properties of the TiAIN/Cu coatings were characterized and analyzed. The results reveal that the coating structure and properties depend on not only the Cu concentration, hut also the deposition condition. The addition of Cu significantly decreases the grain size and weakens the texture in the TiAlN/Cu coatings. With increasing the Cu concentration, the coating hardness decreases slightly from 30.7 GPa of the pure TiAlN coating to 28.5 GPa of the TiAlN/Cu coating with 1.4 at,% Cu. All the TiAlN/Cu coatings present sufficient adhesion strength. In addition, the existing state of additive Cu in the TiAlN/Cu coatings is also investigated.