Protective hard coatings can significantly improve the bottleneck problem of low hardness and poor wear resistance on titanium alloy surface. However, hardness and adhesive strength usually exhibit ...an inverse relationship, which greatly limits its widespread use. In this work, TiC–Fe gradient coating with high hardness and adhesion was successfully fabricated by in-situ solid-phase diffusion method (ISDM) on pure titanium at 1000 °C for 2 h. The average thickness of the coating was approximately 5 μm, and the volume fraction of TiC in the coating was greater than 95 vol%. The grain size of TiC gradually increased from 200 nm at the coating surface to 2 μm towards the substrate. The phase interface and the coating/substrate interface exhibited excellent interfacial bonding at the atomic scale. The novel TiC–Fe gradient coating can simultaneously achieve superior hardness (42.9 ± 2.6 GPa) and elastic modulus (557.4 ± 10.3 GPa) that is mainly dominated by in situ synthesised high volume fraction TiC, as well as high adhesion strength (>225 ± 10 MPa). The increased adhesion strength was attributed to the excellent macro/micro interfaces and gradient transition of the microstructure. The use of ISDM to fabricate TiC–Fe gradient coating on titanium alloy may provide a new strategy to improve the comprehensive properties including hardness, elastic modulus, interfacial adhesion strength, and wear resistance for wider applications.
Carbonate cements are the most abundant authigenic mineral and impact on physical properties greatly in sandstone reservoir. In this paper, Pinghu Formation of Xihu Sag was taken as a target. ...Characteristics, distribution and formation of carbonate cements were investigated via optical microscopy, cathodoluminescence (CL), electron probe and
in-situ
carbon-oxygen isotope. The results showed that carbonate cements varied in types and shapes. Calcite/dolomite mainly present as poikilotopic cements, while ferrocalcite/ferrodolomite/ankerite generally present as pore-filling cements. Carbon isotope (δ
13
C) values of carbonate cements were ranging from −7.77‰ to −2.67‰, with an average of −4.52‰, while oxygen isotope (δ
18
O) values were ranging from −18.94‰ to −12.04‰, with an average of −14.86‰. The δ
13
C/δ
18
O indicated that the paleo-fluid of carbonate cement was mainly freshwater. Organic carbon mainly came from organic matter within mature source rocks, and inorganic carbon came from dissolution of carbonate debris and early carbonate cements. Distinctive δ
13
C/δ
18
O values manifest that carbonate cements with different types formed in different periods, which make different contributions to the reservoir properties. Calcite/dolomite formed during eodiagenesis (70–90°C) and early mesodiagenesis stage (90–120°C), and were favorable to reservoir owing to their compacted resistance and selective dissolution. Ferrocalcite/ferrodolomite/ankerite formed during middle-late mesodiagenetic stage (above 120°C), and were unfavorable to reservoir due to cementing the residual intergranular pores. Hence, in order to evaluate the reservoir characteristics, it is of significantly important to distinguish different types of carbonate cements and explore their origins.
To overcome the disadvantages of low toughness of conventional particle reinforced steel/iron-based composites, a novel niobium-niobium carbide/iron (Nb-NbC/Fe) core–shell rod-reinforced ...cast-iron-matrix composites were fabricated through two-step in situ solid-phase diffusion at 1172°C for 15min, followed by heat treatment at 1120°C for 1, 4, 7, and 10h (1172°C×15min+1120°C×(1, 4, 7, 10h)). The effects of soaking time on the microstructure and mechanical properties of the composites were investigated. Results indicated that the phase composition of the Nb-NbC/Fe core–shell rod-reinforced cast-iron-matrix composites were NbC, Nb, α-Fe and, graphite (G) phases, where Nb existed as core at the center surrounded by NbC/Fe shell. With the extension of the soaking time, the phase composition of the composites did not change, but the thickness of the NbC/Fe shell increased from 90±3μm to 233±5μm. The average hardness of the NbC/Fe shell was 12.86GPa, which was approximately 2.6 times than that of the cast-iron-matrix due to high volume fraction of NbC particles. The yield strength and strain of the composite prepared at 7h reached the maximum value of 1794.4MPa and 11.6%, respectively. The excellent yield strength was attributed mostly to NbC particles, which induced the load-transfer strengthening and the mismatch of thermal-expansion-coefficient strengthening. Meanwhile, the Nb and α-Fe effectively hindered microcrack propagation, which contributed to the reasonable plasticity of the composite.
The coupling relationship between shelf-edge deltas and deep-water fan sand bodies is a hot and cutting-edge field of international sedimentology and deep-water oil and gas exploration. Based on the ...newly acquired high-resolution 3D seismic, logging and core data of Pearl River Mouth Basin (PRMB), this paper dissected the shelf-edge delta to deep-water fan (SEDDF) depositional system in the Oligocene Zhuhai Formation of Paleogene in south subsag of Baiyun Sag, and revealed the complex coupling relationship from the continental shelf edge to deep-water fan sedimentation and its genetic mechanisms. The results show that during the deposition of the fourth to first members of the Zhuhai Formation, the scale of the SEDDF depositional system in the study area showed a pattern of first increasing and then decreasing, with deep-water fan developed in the third to first members and the largest plane distribution scale developed in the late stage of the second member. Based on the development of SEDDF depositional system along the source direction, three types of coupling relationships are divided, namely, deltas that are linked downdip to fans, deltas that lack downdip fans and fans that lack updip coeval deltas, with different depositional characteristics and genetic mechanisms. (1) Deltas that are linked downdip to fans: with the development of shelf-edge deltas in the shelf area and deep-water fans in the downdip slope area, and the strong source supply and relative sea level decline are the two key factors which control the development of this type of source-to-sink (S2S). The development of channels on the continental shelf edge is conducive to the formation of this type of S2S system even with weak source supply and high sea level. (2) Deltas that lack downdip fans: with the development of shelf edge deltas in shelf area, while deep water fans are not developed in the downdip slope area. The lack of “sources” and “channels”, and fluid transformation are the three main reasons for the formation of this type of S2S system. (3) Fans that lack updip coeval deltas: with the development of deep-water fans in continental slope area and the absence of updip coeval shelf edge deltas, which is jointly controlled by the coupling of fluid transformation at the shelf edge and the “channels” in the continental slope area.
To overcome the strength-toughness inversion relationship in steel/Fe matrix composites, a novel W-WC/Fe composite fiber-reinforced Fe matrix composite ((W-WC/Fe)f-IMC) with exceptional strength and ...toughness was fabricated by an in-situ fabrication method combining infiltration and in-situ solid-phase diffusion. The (W-WC/Fe)f-IMC consists of aligned W-WC/Fe composite fibers embedded in an Fe matrix. The W-WC/Fe composite fiber exhibits a characteristic core-shell structure on its cross section, with a resilient metal W fiber serving as the core and a robust annular WC-Fe layer acting as the shell. Due to the inward-outward growth and the gradient microstructure of the WC-Fe layer, the interface bonding strength between the W fiber/WC-Fe layer and the WC-Fe layer/matrix remains excellent. As a result, the (W-WC/Fe)f-IMC achieves an exceptional fracture strain of 35.5 ± 1.3 %, while maintaining high yield strength of 701 ± 16 MPa and ultimate compression strength of 1100 ± 18 MPa, surpassing those of cast Fe, which had values of 26.9 ± 1.1 %, 365 ± 20 MPa, and 834 ± 15 MPa, respectively. The simultaneous enhancement of the strength and toughness in (W-WC/Fe)f-IMC can be primarily attributed to the synergistic coupling effect between the high strength W-WC/Fe composite fibers and the tough matrix. The strategy proposed in this study holds promise as a method to alleviate the trade-off between strength and ductility in steel/Fe matrix composites.
The hardness and adhesion of protective hard coatings to the substrate are the most important parameters that influence the performance of the tool. Herein, we propose an effective strategy, by ...in-situ hot press sintering, to fabricate a novel niobium carbide coating with high hardness and excellent interfacial bond strength on GCr15. The coating is composed of Nb2C, NbC, and α-Fe phases. The volume fraction of niobium carbide (Nb2C and NbC) phases reaches 93%. Along the direction of coating thickness, the grain morphology of niobium carbide changes from equiaxed (Nb2C) to columnar (NbC), and then to equiaxed (NbC), presenting a gradient microstructure. The coating/substrate interface displays an excellent macro/micro interface. The formation of the gradient microstructure is attributed to the nucleation-growth process controlled by the carbon concentration gradient diffusion. The novel gradient coating can simultaneously achieve superhardness (20.2 ± 0.3 GPa) and excellent bond strength (>210 ± 20 MPa). The excellent bond strength is mainly attributed to the in-situ formation of the coating and the gradient microstructures. The tensile test results show that the fracture mechanism of the niobium carbide coating on GCr15 is mainly a brittle fracture of niobium carbide coating and a small amount of coating debonding.
The effects of the addition of Nb and Ti and heat treatment on the microstructure evolution and hardness of the as-cast and directionally solidified NiAl–Cr(Mo) alloy were studied. Nb mainly ...solubilizes in the Cr(Mo) phase while Ti basically solubilizes in the NiAl phase. Precipitated phases of Cr2Nb and Ni2AlTi are formed and mainly distributed at the cell boundary. With the increasing Nb content, the primary Cr(Mo) phase increases significantly and does not show dendritic morphology. The eutectic coupled growth is suppressed and the lamellar microstructure becomes irregular. Fully eutectic microstructure with no primary Cr(Mo) phase is obtained in the directionally solidified NiAl–Cr(Mo)–Nb and NiAl–32Cr–6Mo–1Ti–1Nb alloys while dendrites + eutectic is observed in the directionally solidified NiAl–32Cr–6Mo–3Ti–3Nb alloy. After heat treatment, Nb and Ti are redistributed. The eutectic microstructure becomes relatively uniform and the precipitated phases become fine and dispersed. The addition of Nb and Ti can increase the hardness of the alloy due to the solid solution strengthening and precipitation strengthening. As the Nb content increases, the hardness further increases. The hardness of the directionally solidified alloys is higher than the as-cast alloys attributing to the regular microstructure. After heat treatment, the hardness of the all alloys decreases due to the varying microstructure morphology and phase distribution, especially the coarsening of NiAl precipitates and the existence of dislocations in Cr(Mo) phase.
To overcome the disadvantages of low toughness and low fracture energy of conventional particle reinforced steel/iron-based composites, a novel V8C7-Fe/iron dual-scale composite was designed and ...fabricated via a two-step in situ reaction at 1150 °C for 5 min and 1100 °C for 12 h (denoted as 1150 °C-5 min + 1100 °C-12 h). The composite consists of a bundle-shaped V8C7-Fe dual-scale structure and cast iron matrix. Predominant features of the bundle-shaped V8C7-Fe dual-scale structure, which has a diameter of approximately 3 mm, include a toughness of the α-Fe phase and a high volume fraction of V8C7 particles that have different sizes and morphologies. The interface of the V8C7-Fe dual-scale structure/matrix has distinct gradient distribution characteristics. From the center of the V8C7-Fe dual-scale structure to the matrix, the morphology of the V8C7 particles evolves from nearly spherical to cubic. This is mainly because of changes in the growth environment that lead to the competitive growth between different crystal faces and orientation attachment growth during nucleation and growth. In addition, from the center of the V8C7-Fe dual-scale structure to the matrix, the hardness gradually decreases from 1306 HV0.2 to 410 HV0.2. For the V8C7-Fe/iron dual-scale composite, the yield strength, maximum compressive strength, and maximum compressive strain are approximately 1150 MPa, 1390 MPa, and 15.2%, respectively. Compared to cast iron (420 MPa, 830 MPa and 21.8%, respectively), the V8C7-Fe/iron dual-scale composite achieves both high strength and reasonable toughness.
To improve the mechanical properties of the surface of iron-based alloys, a ZrC–Fe coating is produced on cast ion via in situ solid-phase diffusion (ISSD) at 1130 °C. The coating is completely ...dense, reaching a thickness of approximately 18 μm after 10 h of ISSD. The volume fraction of the ZrC phase in the coating reaches approximately 92.3%. The size of the long axis (short axis) of columnar ZrC particles gradually decreases from approximately 4 μm (1.5 μm) to 1 μm (0.3 μm) as the thickness of the coating increases, displaying a gradient microstructure. The formation mechanism of the coating is mainly attributed to the carbon atoms diffuse into the octahedral vacancies of the zirconium lattice to undergo a diffusion-type solid state phase transformation to form ZrC, and α-Fe phase are distributed among the ZrC particles through the Fe atoms diffusion. Due to the carbon concentration gradient, the nucleation rate is reduced, thereby forming a gradient microstructure on the grain scale. The growth of the coating obeys the growth kinetic model d2=30.5t. In addition, the nanohardness and elastic modulus of the surface of the ZrC–Fe coating reach 29.7 GPa and 425.1 GPa, respectively, showing remarkable improvement compared to those of the cast iron substrate (4.5 GPa and 229.5 GPa, respectively). The fracture toughness gradually increases from 2.9 ± 0.1 MPa m1/2 to 3.6 ± 0.1 MPa m1/2 as the thickness of the coating increases. Moreover, the coating exhibits the superior coating/substrate adhesion. The excellent comprehensive mechanical properties are tightly related to a small amount of high toughness α-Fe phase, high volume fraction of in situ ZrC particles and the gradient change of the ZrC grain scale.
Aiming at the problem of the “inverse relationship” between the hardness (wear resistance) and toughness of the traditional single homogeneous structure coating on the surface of titanium alloy, the ...design and development of a high hardness, high toughness and wear-resistant coating with high reliability and long life is great significance for expanding the application of titanium alloy. Inspired by the microstructure of high-performance organisms in nature, the design ideas of multi-phase, multi-level and multi-scale hybrid reinforcement are used to give full play to the synergy, coupling and multi-functional response mechanism between different phases in the coating to obtain the wear-resistant coating with high hardness and high toughness. This article mainly reviews the research progress of several typical wear-resistant coatings with high hardness and high toughness on the surface of titanium alloy from the aspects of preparation process, microstructure, mechanical properties, and strengthening-toughening mechanisms, such as gradient structure coating, multi-scale structure coating and layered structure coating. On this basis, it is pointed out that in the future, the wear-resistant coating with high hardness and high toughness on the surface of titanium alloy should develop in the direction of developing intelligent manufacturing technology, optimal design and precise tailoring of microstructural architectures, and constructing the numerical simulation technology of composition-structure-performance. Furthermore, the authors propose the technology route for the controllable preparation of wear-resistant coating with high hardness and high toughness on the surface of titanium alloy, namely, through the coordination of theoretical calculations, numerical simulations, and intelligent manufacturing technologies to achieve the controllable preparation of the optimal structural coatings on the surface of titanium alloy, establish the functional relationship between composition-structure-performance, and accurately reveal the mechanism of strengthening and toughening, which provides a new idea for alleviating and balancing the bottleneck of the “inverse relationship” between hardness (wear resistance) and toughness, and achieving the preparation of titanium-based surface composite with excellent comprehensive properties.
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