Papers by Keyword: Lamellar Structure

Abstract: Heat-resistant Ti-Al-Nb-Zr alloys, which don’t contain Sn, have been designed to obtain good oxidation resistance above 600 °C. In addition, to design Ti alloys with best balance of creep and fatigue properties, prior β grain size which affects fatigue properties and lamellar microstructure which affects creep properties were controlled by heat treatment. In the present study, the effect of microstructure on creep properties of one of the alloys, i.e., Ti-7.5Al-4Nb-4Zr alloy, with the bimodal (B), the lamellar structures in small prior β grains (L_S), and the lamellar in large prior β grains (L_L) were investigated at 600 °C. The creep deformation mechanism for each microstructure was a power-law creep. However, the creep life varied depending on the microstructures. The longest creep life was obtained in L_S with prior β grain size of 90 μm and interlamellar spacing of approximately 10 μm, while the shortest creep life was obtained in L_L with prior β grain size of 550 μm and fine interlamellar spacing of less than 2~3 μm. This suggests that creep life is more affected by interlamellar spacing than by prior β grain size.

Abstract: Ni-Cr binary alloys containing high amount of Cr demonstrate gamma/alpha-Cr lamellar structure by discontinuous precipitation (DP) reaction from grain boundary. The mechanism of DP reaction is caused by supersaturated Cr in the gamma phase. Supersaturated Cr concentration influences the driving force for the DP reaction and the lamellar spacing. Moreover, the Ni-based alloys with high Cr, containing Al, significantly increase the hardness and strength due to the very narrow lamellar structure. Al addition brings on Ni consumption in the matrix by precipitation of the gamma prime phase. Therefore, Cr supersaturates dramatically in the matrix. The wrought Ni-Cr-Al alloy, Ni-38Cr-3.8Al (mass%) , reaches extremely high tensile strength, which is over 2 GPa, after annealing treatment. Even though chemical composition of Ni-38Cr-3.8Al is simple, the microstructure is complex because it consists of the gamma/alpha Cr lamellar structure with the fine gamma prime particles. Therefore, in this study, we investigated the influence of Cr concentration on the cellular precipitation behaviour. In order to understand the influence of Cr concentration, Ni-34, 36 and 38Cr-3.8Al alloys were prepared. Forged bars were subjected to solution treatment in the gamma single phase region. Subsequently, the alloys were aged from 873K to 1073 K for various times. The cellular precipitation reaction is suppressed by a decrease in Cr concentration, particularly at low temperature annealing treatment condition. The hardness is low in lower Cr concentration alloys in all range of annealing treatment temperature. These results indicate that Cr concentration remarkably affects the driving force for the DP reaction.

Abstract: Effects of Sr levels on microstructure of the LPSO structure-containing Mg_98.5-xNi_0.5Y_1.0Sr_x(x=0, 0.05, 0.10, 0.20 at.%) alloy were studied by SEM/EDS and XRD. Without Sr addition, the Mg_98.5Ni_0.5Y_1.0 alloy consists of α-Mg and LPSO structure and the block LPSO structure is distributed along the grain boundary. After adding 0.05 at.% Sr element into Mg_98.5Ni_0.5Y_1.0 alloy, the amount of dendrites decreased. With the increase of Sr content, the size of α-Mg grains decreases firstly and then increases. Meanwhile, the LPSO structure is refined. The addition of Sr element also results in the obvious increment of the amount of lamellar structure, which stretched from the grain boundary to the matrix. The excessive Sr in high Sr-content alloys participates in the form of Mg-Ni-Y-Sr compound, which is distributed in the vicinity of LPSO structure. In addition, the Sr can also promote the formation of Ni-rich and Y-rich phases.

Abstract: The paper presents changes in UHMWPE morphology and structure caused by irradiation with an electron beam and plastic deformation. The input material consisted of two grades of polyethylene, i.e. GUR 1050 and GUR 1020 (Poly Hi Solidur Medi TECH), used for producing the bearing components of endoprostheses applied in total joint alloplasty. Tests involved three groups of samples: the ones subjected to modification through radiation (N) only, those modified by plastic deformation before (ON) and after (NO) irradiation with an electron beam (N). The obtained variants were subjected to comprehensive morphological and structural tests, which made it possible to document changes in the lamellar structure (SEM) and orientation of the crystalline structure (SAXS) as well as to determine the content of the crystalline phase (DSC) and to define crosslinking density.

Abstract: Combined strengthening-toughening technologies of several high property titanium alloys, such as TC4-DT, TC6, TC18, TC21 for aviation uses, have been studied via purification, quasi-b heat treatment, quasi-b forging and grain refinement. The effects of microstructure parameters of lamellar structure, basket-weave structure, refined grain structure etc. on the comprehensive mechanical properties of titanium alloys have been analyzed. The results have shown that, to acquire highly comprehensive static mechanical properties and excellent damage tolerance properties, quasi-b treatment and purification processing should be used for medium strength titanium alloys to get high ductility lamellar structure, while quasi-b forging processing be utilized for high strength titanium alloys to obtain high ductility basket-weave structure. Grain refinement processing is very necessary for both the strength levels of titanium alloys.

Abstract: Elasto-plastic tensile deformations in pearlite lamellar and two-colony structures are studied by finite element analyses to investigate the effects of lamellar thickness ratio and difference of lamellae orientation of two colonies in pearlite microstructure. The results obtained from plastic strain distributions in lamellar and colony structures show that plastic deformation in cementite lamellar stabilized when ferrite lamellar is thicker than cementite lamellar thickness and plastic strain concentrates when the difference between cementite lamellar orientation in two colonies are larger than 45°.

Abstract: TiB₂-TiC, TiB₂-TiN and TiB₂-TiC_xN_1-x composites were prepared by arc-melting mixtures of TiB₂, TiC and TiN powders. 28TiB₂-72TiC (mol%) composite showed a lamellar eutectic structure, while 55TiB₂-45TiN (mol%) composite with a lamellar structure consisted of TiB₂, TiN and TiB. 36TiB₂-44TiC-20TiN (mol%) was a quasi-binary eutectic composite having a rod-like structure.

Abstract: The effects of processing conditions on the structure of polypropylene fibrillated fibres were studied using a combination of wide- and small-angle X-ray scattering methods. In particular the impact of selected stages of processing on the crystalline and lamellar structure of PP were analyzed. It was stated that crystalline phase is built from α crystals. The crystallinity index as well as the Herman orientation factor of the crystalline phase is found to have a correlation only with the draw ratio of the PP film. The lamellar structure also changes with the draw ratio.

Abstract: The paper presents changes in UHMWPE morphology and structure induced by exposure to a beam of electrons and thermal processing applied after the modification through irradiation. Two groups of samples were tested: those that underwent modification through irradiation only and those that underwent a sequential process which consisted of radiation modification and thermal processing. The obtained variants were subjected to comprehensive morphological and structural tests, which made it possible to: document changes in the lamellar structure (SEM); determine the content of crystalline phase (DSC); determine the degree and density of crosslinking; state the degree of polymer oxidation (FTIR); examine the influence of the irradiation dose on the intensity of free radicals occurrence (EPR) and to determine the effectiveness of their elimination using recrystallisation in an oxygen-free environment.

Abstract: In this paper, an attempt has been made to determine the changes in the structure of UHMWPE under the influence of deformation, which can be the cause of the decrease of functional properties. It has been found that the degree of cross-linking slightly changes due to operational loads (deformation ef=0.15-0.6). The deformation leads, however, to the systematic lowering of the degree of crystallinity and an insignificant decrease of lamella width. Tests of wide- and small-angle X-ray scattering (WAXS, SAXS) prove that this is the result of operational deformation causing a rather weak texture of crystals and the fragmentation of some lamellae. Anisotropy of the lamellar structure also takes place, which changes 2D SAXS images into ellipses with a rapidly growing axial ratio with ef value.