Search results

A large number of studies have been carried out in the last years to develop new candidates to replace the nowadays used metallic biomaterials [4–8].
It can be seen that from the grain boundaries small martensitic needles, corresponding to the martensitic α` phase grow into the β grains.
After annealing only the boundaries of former β grains are visible.

The phase boundaries act both as source and sink for point defects, and the grain boundaries in an intermediate phase, formed during annealing, may alter the overall diffusion rate in the system.
These pieces were encapsulated in quartz tubes in He atmosphere at a residual pressure of about 16 kPa and annealed at 1223 K for 72 h to homogenise the materials and to form stable coarse grained structure, which reduces the contribution of grain boundary diffusion in the diffusion annealing stage.
The standard PAP correction program was used for atomic number (Z), absorption (A), and fluorescence (F) corrections.

Surface of the specimens was ground with waterproof SiC paper to #1200, and then polished with alumina power of 1μm grain size.
Surface morphologies of the TiN coated titanium and duplex treated titanium were shown in Fig 1, it could be observed that the TiN grains were triangular pyramid in shape from both SEM micrographs, however, in the case of duplex treated samples, the grains size were larger and the structure was compact and dense compared with TiN coated samples.
In the case of duplex treatment, more number of micropores are blocked, this improves the corrosion resistance of the duplex treated samples compared with single TiN layer coated samples.

The mechanism most widely accepted explains the improvements observed in high temperature oxidation of alloys containing RE, as being due to diffusion of the RE ions to oxide scale grain boundaries and blocking of alloy cation diffusion along these paths [17-20].
Specimens of the alloy containing La2O3 concentrate did not spall after 100h at 900ºC, but a number of surface cracks were seen, as shown in Fig. 3c.
In Fe-Cr alloys without reactive elements, Cr2O3 grows by diffusion of both oxygen and Cr along the grain boundaries, and the oxide layer is thick [21].
The RE ions segregate to the grain boundaries of the alloy and the oxide scale, close to the metal/oxide interface [8].

For high solid fraction materials, Lalli[3] and Charreyron and Flemings[4] characterized the deformation behavior of semi-solid material with D’Arcy’s law for liquid phase flow and compressible plastic deformation theory for solid grains.
This was because the higher deformation temperature, the thicker the thin film of liquid phase in grain boundary, and then the grain shape near to spherical, which made it slip and turn easier, the deformation resistance decreased.
Table 3 Multiple regression and test results of constitutive equation Parameters Value Standard Error t-Value Prob>|t| A Intercept 20.9018 0.874 23.9166 0 B -0.2469 0.01783 -13.849 0 C 0.0629 0.00724 8.6791 1.28E-12 D -0.0215 0.00104 -20.695 0 Table 4 Statistical information of multiple regression Statistics A Statics A Number of Points 72 R-Square(COD) 0.915 Degrees of Freedom 68 Adj.

Disadvantage of GMA process is longer completion time since more number of arc passes are required to complete a joint and for SAW process it is coarse grained brittle structure with a low strength.
The test specimen was high-strength; thermo- mechanically rolled fine grained structural steels.
Conclusion It has been the objective of this research project to investigate the applicability of laser GMA hybrid welding method for the production of thick-walled mechanical pipes made of fine grained CMn steels.

Tab. 2.2 Orthogonal test results of composite electrodeposition test number factor index A(A/dm2) B（g/l） C（g/l） D(%) E(W) particle content(wt%) 1 1(2) 1(5) 1(5) 1(20) 1(120) 1.09 2 1(2) 2(10) 2(10) 2(30) 2(180) 1.82 3 1(2) 3(15) 3(20) 3(40) 3(240) 2.67 4 1(2) 4(20) 4(40) 4(50) 4(300) 2.19 5 2(3) 1(5) 2(10) 3(40) 4(300) 1.37 6 2(3) 2(10) 1(5) 4(50) 3(240) 1.42 7 2(3) 3(15) 4(40) 1(20) 2(180) 3.29 8 2(3) 4(20) 3(20) 2(30) 1(120) 2.47 9 3(4) 1(5) 3(20) 4(50) 2(180) 2.32 10 3(4) 2(10) 4(40) 3(40) 1(120) 2.77 11 3(4) 3(15) 1(5) 2(30) 4(300) 2.81 12 3(4) 4(20) 2(10) 1(20) 3(240) 2.67 13 4(5) 1(5) 4(40) 2(30) 3(240) 3.01 14 4(5) 2(10) 3(20) 1(20) 4(300) 1.78 15 4(5) 3(15) 2(10) 4(50) 1(120) 2.28 16 4(5) 4(20) 1(5) 3(40) 2(180) 2.69 K1 7.77 7.79 8.01 8.83 8.61 K2 8.55 7.79 8.14 10.11 10.12 K3 10.57 11.05 9.24 9.50 9.77 K4 9.76 10.02 11.26 8.21 8.65 k1 1.94 1.95 2.00 2.21 2.15 k2 2.14 1.95 2.04 2.53 2.53 k3 2.64 2.76 2.31 2.38 2.44 k4 2.44 2.51 2.82
Comparing Figure 2.1(a) with Figure 2.2(a), we can see that although the surface roughness of the nanocomposite coating obtained under the conditions of A2B3C4D1E2 is fine, the grain is coarse and the microstructure is less compact; however the surface morphology of the nanocomposite coating obtained under the conditions of A3B3C4D1E2 looks smooth, dense and compact, and the grain is further refined.
(3) The particle contents in the binary Ni-TiN-CeO2 nanocomposite coatings prepared under the optimum process conditions are: CeO2 3.3wt%, TiN 4.4wt%, and the obtained coatings show a smooth surface with fine and compact of Ni matrix, at the same time, TiN and CeO2 nanoparticles distribute uniformly in it and the grain size was refined.

It can be seen that without the addition of V, the amount of austenite is higher, and the carbides appear as thick lath; with the increase of the content of V, primary austenite grain size is refined distinctly, the amount of austenite dendrite decreases significantly and the eutectic carbide changes from thick lath to thin lath, and rosette-like morphology.
Vanadium is a kind of expanding austenite area element, with the addition of V increases the austenite dendrite quantity during the initial crystal crystallization process of the high chromium white cast iron, thus the austenitic grain decreased.
It can be seen that the microstructure is refined and a large number of secondary carbides precipitated from the primary austenite matrix of heat treatment cast iron, the etched secondary carbides appear bright in the microstructure.
Thirdly, this heat treatment can make more martensite transformation and make the alloy present a refiner matrix, and a refiner matrix implies a finer grain strengthening effect, which would contribute to wear resistance improvement.

Experimental procedures PVD coatings of the 3rd generation, types duplex AlXN3 (X=Cr; CrN layer+Al/CrN nanomultilayer+AlN layer) and duplex nACRo3 (CrN+AlCrN+nACRo nanocomposite top layer; nanocomposite=nanocrystaline grains are embedded into an amorphous matrix) were deposited onto a steel substrate of hot work steel Böhler W302, with the following chemical composition: 0.39 % C, 1.10 % Si, 0.40 % Mn, 5.20 % Cr, 1.40 % Mo, 0.95 % V.
In the upper zone one can observe fine equiaxial grains of AlN, the zone below the upper one consists of nano-multilayers, the third zone is adhesive CrN layer, and the plasma-nitrided layer is the one closest to the substrate.
However, in the nano-multilayers of duplex AlXN3 coat (Fig. 4) and in the top nanocomposite layer of duplex nACRo3 coat (Fig. 10) there are visible compactness failures, i.e. defects caused most likely by generally recognized the presence of a high number of residual stresses in these coatings, related to the technology of their deposition or polycomponent composition of elements.
The presented paper focused on the study and documentation of surface morphology of coatings and the structure of cross sections, employing Dual Beam FIB/SEM system with following conclusions: - The structure of the duplex AlXN3 coating consisted of four zones: fine equiaxial grains of AlN in the upper zone, nano-multilayers AlN/CrN in the central zone followed by CrN adhesive layer, and the lower plasma-nitrided layer deposited on the substrate.

Along with a number of positive technical properties, gypsum materials have the following disadvantages: relatively high brittleness, low softening coefficient, high creep of gypsum concrete in damp operating conditions [5].
Volcanic ash from the Zayukovskoye field with a maximum grain size of 0.14 mm was used as a filler and an active mineral additive.
At the same time, the influence of the grain size composition of the ash on the gypsum-cement-pozzolanic composite properties was studied.
To study the fiber reinforcement parameters (diameter and length) influence on the strength properties of fine-grained concrete, a second-order rotatable plan of the type of regular hexagon with central points was implemented [13].