Phase Grain Size Research Articles

Mechanochemical study of a novel Magnesium alloy with trace addition of Gd, Nd, Ce, and La rare-earth and Sr elements

Mg-Zn-Ca-Mn materials micro-alloyed by Gd, Nd, Ce, and La rare-earth and Sr alkaline elements were developed. Optical and scanning electron microscopy, X-ray diffraction spectroscopy, tensile test, immersion, and electrochemical tests were applied to analyze microstructure, mechanical properties, and corrosion behavior. While the development of the equiaxed grain structures were observed in all the alloys, the Gd-containing alloy showed the smallest grain size and lowest fraction of second phases, which resulted in the highest yield and ultimate tensile strength of 310.0 ± 14.1 and 370.4 ± 41.6 MPa, respectively. Moreover, the corrosion studies also indicated the lowest rates in the Gd, and Nd-containing alloys, with the rates of 3.6 ± 2.5 and 3.9 ± 0.2 mm/y, respectively. The mechanisms of microstructure evolution, strengthening and corrosion behavior were discussed.

Effect of binder content and sintering time on the microstructure and mechanical properties of gradient cemented carbides with Ni binder

Replacement of Co by alternative Ni binder in gradient cemented carbide is an effective way to reduce the health concerns associated with Co powders. In the present work, gradient cemented carbides with different Ni contents and gradient sintering times were prepared by traditional powder metallurgy with a two-step sintering method. The microstructure of cemented carbide including the gradient layer formation was analyzed by XRD, SEM, EDS, TEM, and EBSD. The thickness of the gradient layer is almost proportional to the square root of sintering time, indicating that the gradient layer formation is a diffusion-controlled process. The atomic migration can be accelerated to form a thicker gradient layer with the increase of the binder content. The coherent interface of the Ti(C, N) core-rim structure for the gradient cemented carbides with Ni binder was revealed. With the increase in binder content, the average grain size of the WC phase is increased. The hardness and fracture toughness of the cemented carbides were also studied and analyzed according to the crack propagation behavior and the distribution of dislocation and stress indicated by KAM and GND. The variation of the hardness and the fracture toughness with the sintering time is mainly related to the density and the grain size of hard phases, while the change of the mechanical properties along with the Ni content probably results from the local dislocation density and the stress in the cemented carbides. The cemented carbide can obtain a good combination of hardness and fracture toughness with 10 wt% Ni gradient sintered for 2h.

Dependences of Magnetic Properties on the Grain Size and Hard/Soft Magnetic Phase Volume Ratio for Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe Nanocomposites.

The magnetic properties of magnetic nanocomposites consisting of hard and soft magnetic phases are dependent not only on the intrinsic properties but also on the grain structure and volume ratio of the two phases. In this study, we performed a systematic micromagnetic simulation on the magnetic properties of Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe nanocomposites. The volume fractions of the hard magnetic Nd2Fe14B or Ce2Fe14B phase were varied from 80% to 40%, and the grain sizes of the hard magnetic phase and the soft magnetic α-Fe phase were changed independently from 10 nm to 40 nm. The results show that when the grain size of both hard and soft phases is 10 nm and the volume fraction of the hard phase is 70%, the highest maximum magnetic energy product can be obtained in both Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe nanocomposites. The hard magnetic properties of Ce2Fe14B/α-Fe nanocomposite decrease significantly when the volume fraction of the α-Fe phase exceeds 30%. However, for the Nd2Fe14B/α-Fe system, this situation only occurs when the α-Fe volume fraction exceeds 40%. The reason for this is not only because of the low anisotropic field and the smaller exchange coupling length between the soft and hard magnetic phases, but also because of the lower saturation magnetization of the hard phase. The grain size has greater effects on the magnetic properties compared to the volume fraction of the hard magnetic phase. The main reason is that as the grain size increases, the remanence of the nanocomposite decreases sharply, which also leads to a rapid decrease in the maximum magnetic energy product. The simulation results on the effects of phase ratio and grain size have been verified by experiments on melt-spun Ce2Fe14B/α-Fe alloys with various compositions prepared by melt-spinning followed by annealing for various lengths of time. Due to the influence of demagnetization energy, the hard magnetic phase with high saturation magnetization is preferred for the preparation of high-performance nanocomposite magnets.

Simultaneously enhanced piezoelectric response and depolarization temperature in BNT-7BT ceramics with simple composition via optimizing sintering temperature

For (Bi0.5Na0.5)TiO3-based ceramics, one of the obstacles limiting their actual application is the incompatibility of a large piezoelectric response d33 with a low depolarization temperature Td. In this work, a high d33 of 186 pC/N and a Td of 133 °C are achieved simultaneously in unmodified 0.93(Bi0.5Na0.5) TiO3–0.07BaTiO3 (BNT-7BT) ceramics only via optimizing sintering temperature. Structural and microstructural analyses show that grain size and relative content of P4bm and R3c phases in BNT-7BT ceramics can be regulated by tuning the sintering temperature (Tsinter = 1100 °C, 1120 °C, 1140 °C, 1160 °C, and 1180 °C). Thus, high sintering temperature is not only able to increase the grain size to promote the domains switching for higher the piezoelectric response, but also to enhance the ratio of R3c/P4bm phase so as to improve ferroelectric-relaxor transition temperature that defer the depolarization. Hence, the present work provides a simple and effective method for optimizing the piezoelectric properties of (Bi0.5Na0.5)TiO3-based ceramics.

Mechanical properties and biocorrosion behaviour of as-cast Zn-xCu-Sr alloys for cardiovascular bioabsorbable devices

ABSTRACT In this study, the mechanical and biocorrosion behavior of as-cast Zn-xCu-0.1Sr (x = 1, 2, and 3wt%) alloys for potential application was studied. The microstructure, mechanical properties, and in vitro degradation of Zn-xCu-0.1Sr alloys were investigated. The results show that as Cu content increased from 1.0 to 3.0wt%, the number of CuZn5 phases increased and the average grain size of CuZn5 phases increased from 6.96 μm to 10.92 μm. The 2wt% addition of Cu resulted in the best mechanical properties with 129.4 MPa in ultimate tensile strength and 108.4 MPa in yield strength. Furthermore, the higher corrosion rate was experienced in the alloys with higher Cu content after immersion. Zn-xCu-0.1Sr alloys all presented appropriate in vitro degradation rates in a basically uniform degradation mode. The strength, ductility and biocorrosion property exhibited by the Zn-2Cu-0.1Sr alloy compositions make it a promising candidate for cardiovascular stent applications.

Effects of the Parent Alloy Microstructure on the Thermal Stability of Nanoporous Au.

Nanoporous (NP) metals represent a unique class of materials with promising properties for a wide set of applications in advanced technology, from catalysis and sensing to lightweight structural materials. However, they typically suffer from low thermal stability, which results in a coarsening behavior not yet fully understood. In this work, we focused precisely on the coarsening process undergone by NP Au, starting from the analysis of data available in the literature and addressing specific issues with suitably designed experiments. We observe that annealing more easily induces densification in systems with short characteristic lengths. The NP Au structures obtained by dealloying of mechanically alloyed AuAg precursors exhibit lower thermal stability than several NP Au samples discussed in the literature. Similarly, NP Au samples prepared by annealing the precursor alloy before dealloying display enhanced resistance to coarsening. We suggest that the microstructure of the precursor alloy, and, in particular, the grain size of the metal phases, can significantly affect the thermal stability of the NP metal. Specifically, the smaller the grain size of the parent alloy, the lower the thermal stability.

Microstructure evolution and enhanced fatigue behavior in the Mg-10Li-5Zn-0.5Er alloys micro-alloyed with Yb

In this paper, (0.2–1 wt%) Yb was added to improve the tensile properties and high-cycle fatigue behavior of the as-cast and as-extruded Mg-10Li-5Zn-0.5Er alloys. It is found that Yb mainly affects the mechanical properties of the alloy by changing the grain size, type and morphology of the second phases. Yb mainly exists in the formation of Mg2Yb and Mg-Zn-Yb phases in the metallographic structure. With the addition of Yb, the grains are refined and these Yb-containing phases replace the large-sized MgLiZn phase to be enriched at the grain boundaries. While the addition of excess Yb reduces the number of small-sized MgLiZn phases in the grain, thus reducing the alloys’ mechanical performance. After extrusion, the small-sized MgLiZn phase is refined and the number increases, which effectively improves the tensile and fatigue strength of the alloy. The fatigue strength is mainly affected by the number and morphology of the second phase, positively correlated with the strength. Balanced in grain size and number and size of second phases, the extruded alloy with 0.2Yb added exhibits excellent mechanical properties with the yield strength, ultimate tensile strength and elongation of 292 MPa, 303 MPa and 11.7%, and an fatigue strength of 130 MPa.

Improving microstructure and corrosion resistance of LPSO-containing Mg–Y–Zn–Mn alloy through ECAP integrated with prior solution treatment

Unique Mg-RE (rare earth) alloys with long-period stacking ordered (LPSO) structures have attracted extensive attention for their excellent mechanical properties and bright prospects. Thus it is urgent to improve their corrosion resistance simultaneously. The present work focused on the improvement of microstructure and corrosion behaviours in new Mg-2.2Y-1.1Zn-0.4Mn (wt. %) alloys with mixed LPSO phases through warm equal-channel angular pressing (ECAP) integrated with prior solution treatment (ST). The results show that the multi-pass ECAP process optimizes the grain size and distribution of mixed LPSO phases, which improves the corrosion resistance of the alloy. During the integrated ECAP processing, the massive 18 R phase was broken from 100 μm (as-cast) to 5–8 μm (12 passes), and the precipitated 14H phase was more uniformly distributed in the fined α-Mg matrix. Accordingly, the corrosion resistance of the LPSO-containing samples from 0 to 8 ECAP passes increased for a more uniform and more refined structure. In contrast, the corrosion resistance improvement of the 12-pass ECAP one was reduced slightly for weakened 18 R barriers.

In situ reinvestigation of reaction phase A plus high-pressure clinoenstatite to forsterite plus water in the system MgO-SiO<sub>2</sub>-H<sub>2</sub>O (MSH)

Abstract. The dehydration reaction of phase A + high P clinoenstatite to forsterite + water was experimentally investigated at water-saturated conditions in the pressure range between 7.0 and 10.0 GPa by in situ reversal runs in a multi-anvil press at the synchrotron source of PETRA III in Hamburg. By using closed watertight X-ray transparent Ti capsules, its position is determined by reversal brackets at 8.3 GPa (700–760 ∘C), 8.6 GPa (700–740 ∘C), and 9.8 GPa (750–800 ∘C); thus, the equilibrium of the reaction corresponds ideally to the data reported by Wunder (1998). Optical investigations of the quenched product phases show strong grain coarsening of phase A and clinoenstatite, whereas nucleated forsterite from the breakdown of the aforementioned phases is very fine grained. This corresponds to recent experimental observations that the grain size of phases formed in hydration reactions are significantly larger than those from dehydration reactions. In addition, we performed three time-dependent in situ experiments at 9–10 GPa and 800–870 ∘C and monitored the reaction progress every 10 min to determine the kinetics of the forsterite formation from phase A + high P clinoenstatite. The growth of forsterite at these P–T conditions, already visible after 10 min, confirms the results of the bracketing experiments. However, the reaction is extremely slow, and even after more than 3 h, significant amounts of phase A and high P clinoenstatite are still present. This is in contradiction to other dehydration reactions of former experimental studies, e.g. the fast dehydration of serpentine, which completely dehydrates within 3 h, even at much lower temperatures, closely overstepping serpentine stability. Despite its reaction sluggishness, which would contradict the concept of earthquake initiation, the observed formation of nano-sized forsterite as a dehydration product may still indicate the potential of this reaction to cause mechanical instabilities and, thus, seismicity within cold subduction zones at depths of the Earth's mantle. Additionally, at depths exceeding serpentine dehydration, the phase A + high P/low P clinoenstatite breakdown to forsterite + water might induce geochemical and geophysical processes, including the formation of low-velocity zones within the overlying mantle wedge from the large amounts of fluid liberated by this water line reaction. After the breakdown of antigorite, the assemblage phase A + clinoenstatite might act as a bridge to transport water to larger depths during cold subduction, followed by the formation of other hydrous high P phases.

Corrosion behaviors at different temperature based on the ultrafine-grained structure of Al-Fe alloy

Electrochemical tests and immersion experiments were employed to investigate the corrosion behaviors of the Al-Fe alloy (AA8176) processed by equal channel angular pressing (ECAP) in 3.5 wt% NaCl solution at different temperature (25 °C and 0 °C). It was worked out that after ECAP, with the reduction of grain size, the fragmentation and uniform distribution of precipitated phases increased the number of pitting corrosion but reduced its size, the increase of grain boundary density and the reduction of precipitated phase aggregation decreased the degree of intergranular corrosion. AA8176 changed from local corrosion to uniform corrosion, which provides a new idea to improve the corrosion resistance of Al-Fe alloys.

Inhomogeneous microstructure and properties along the thickness of stir zone in friction stir welded SAF 2507 super duplex stainless steel joint

In the present study, the microstructural inhomogeneity along the thickness of SZ in the SAF2507 SDSS FSW joint and its effect on the mechanical properties and corrosion resistance were investigated. The results suggested that a significant temperature gradient was existed along the thickness of SZ and the biggest peak temperature difference between the top and bottom reached up to 446.9 °C at 700 rpm. Whatever the rotational speed, the unexpected phase transformation of ferrite to austenite were both generated in the top SZ with thickness of 20 μm and 38 μm at 350 and 700 rpm, respectively, which confirmed the highest corrosion resistance on the top while significantly deteriorated the property of resistance to stress corrosion cracking. The inhomogeneous grain size and grain misorientation distributions of the constituent phases in the SZ along the thickness direction were synergistically determined by the dynamic recrystallization and subsequent grain growth. The grain size distribution combined with phase transformation contributed to the variation of microhardness in the vertical SZ. The longitudinal tensile test results showed that a good combination of strength and ductility with higher YS and UTS of 596 and 830 MPa respectively as well as slightly lower El of 31.5% comparable to that of the BM, was obtained for the longitudinal tensile specimen derived from the middle part of whole joint. Such results can be attributed to uniform, balanced and refined microstructure with reasonable grain size at the middle of SZ, eventually resulting in the corresponding transverse tensile sample fractured at BM.

Magmatic and hydrothermal evolution of mafic pegmatites and their host basalts, Paraná Large Igneous Province, Brazil

The high-Ti Paranapanema sequence in the Paraná Large Igneous Province consists of a succession of pahoehoe lava flows. Some of these flows host mafic segregation structures, such as horizontal pegmatitic sheet layers and vesicular cylinders. Geochronology, whole-rock and mineral chemistry of two pegmatite occurrences and their host basalts permit characterizing crystal-melt segregation processes that occur during magmatic differentiation after lava flow emplacement. The mineralogy of the pegmatites is similar to that of the host basalts, and it includes plagioclase, pyroxene and titanomagnetite-ilmenite crystals; the only observable difference is the coarser grain size of primary phases and an increase in the volume fraction of clay minerals derived from glass devitrification and vesicle infilling in the pegmatites (~15 vol% clay in the pegmatites vs. ~6 vol% clay in the basalts). The pegmatites from both sites are more fractionated than the enclosing lavas and are enriched in TiO2, FeOtotal, K2O, P2O5 and incompatible trace elements (e.g., Ba, Rb, Nb, Hf, Y, Zr, La, Ce, Yb). Thermodynamic modeling of whole-rock compositional data suggests that the Barracão pegmatites were formed after ~8–27 wt% fractional crystallization of the host basalt, whereas the Capanema pegmatites formed after ~38–43 wt% fractional crystallization of the host basalt. 40Ar/39Ar geochronology indicates slight yet significant age differences between plagioclase phenocrysts from the pegmatites and whole-rock fragments from the enclosing lavas (Capanema: 133.56 ± 0.52 pegmatite vs. 134.30 ± 0.46 Ma enclosing lava; Barracão: 133.23 ± 0.88 pegmatite vs. 134.49 ± 0.31 Ma enclosing lava). These age differences likely result from hydrothermal alteration of the plagioclase phenocrysts (e.g., secondary albite and K-feldspar), and they are not due to resolvable differences in crystallization age. Smectite-celadonite aggregates recovered from the Capanema basalt suggest that hydrothermalism occurred at 123.18 ± 0.61 Ma, approximately ten million years after rock crystallization.

Modification of microstructure of LD slag for recovery of hybrid flux material

The Basic Oxygen Furnace steel making process produces BOF slag (LD slag) at a rate of about 125 kg/t. The LD slag contains about 18% Fe in wustite and dicalcium ferrite and about 45% CaO. These minerals are an excellent source of alternative flux material for the steel industry. Through slag modification and in-depth characterization studies, investigations were carried out to develop a material that could be utilized as an alternative flux material. Detailed characterization studies were conducted using SEM-EPMA and XRD to identify the changes in the crystal structure, phase distribution, grain size and liberation size of minerals. The grain size of phases was found to be between 10-150 ­­­­­µm for normally cooled slag and 20-250 µm for slowly cooled slag. It was also shown that slow cooling promotes the formation of an additional phase which is essentially the dicalcium silicate phase (C2S) with some amounts of FeO and MgO in the crystal lattice. Overall, it was observed that about 50% of the LD slag could be recovered as alternative flux material containing approximately 30% CaO and 30% Fe content. This alternative flux material is an excellent source of material for use in steel industries because of its low melting slag formation.

Effect of heat treatment on the FeCoCrNiMnAl high-entropy alloy cladding layer

ABSTRACT FeCoCrNiMnAl high-entropy alloy cladding was fabricated on the surface of 4Cr5MoSiV1 substrate by laser cladding technology. The microstructure, hardness and wear resistance of the cladding layer were systematically investigated using electron back scattered diffraction, transmission electron microscope, microhardness and wear tests. The was no obvious change in the grain size, type and proportion of phases (dual-phases of face centred cubic and body centred cubic ) in the FeCoCrNiMnAl coating after heat treatment at 600°C for 100 h. The recrystallization induced by the heat treatment decreased the density of dislocations. Finally, the microhardness and wear resistance of the FeCoCrNiMnAl cladding layer decreased by 9.2% and 11.7%, respectively, after the heat treatment. Nevertheless, it still fulfils the application requirements.

The influence of intergranular and interphase boundaries and δ-ferrite volume fraction on hydrogen embrittlement of high-nitrogen steel

We study the effect of grain size of austenitic and ferritic phases and volume fraction of δ-ferrite, which were obtained in different solution-treatment regimes (at 1050, 1100, 1150 and 1200 °C), on hydrogen embrittlement of high-nitrogen steel (HNS). The amount of dissolved hydrogen is similar for the specimens with different densities of interphase (γ-austenite/δ-ferrite) and intergranular (γ-austenite/γ-austenite, δ-ferrite/δ-ferrite) boundaries. Despite, the susceptibility of the specimens to hydrogen embrittlement, depth of the hydrogen-assisted surface layers, hydrogen transport during tensile tests and mechanisms of the hydrogen-induced brittle fracture all depend on grain size and ferrite content. The highest hydrogen embrittlement index IH = 32%, the widest hydrogen-affected layer and a pronounced solid-solution hardening by hydrogen atoms is typical of the specimens with the lowest fraction of the boundaries. Even though fast hydrogen transport via coarse ferritic grains provides longer diffusion paths during H-changing, the width of the H-affected surface layer in the dual-phase structure of the HNS specimens is mainly determined by the hydrogen diffusivity in austenite. In tension, hydrogen transport with dislocations increases with the decrease in density of boundaries due to the longer dislocation free path, but stress-assisted diffusion transport does not depend on grain size and ferrite fraction. The contribution from intergranular fracture increases with an increase in the density of intergranular and interphase boundaries.

Effect of Synthesis Method of Nickel–Samarium-Doped Ceria Anode on Distribution of Triple-Phase Boundary and Electrochemical Performance

Two-dimensional (2D) electron back scattered diffraction (EBSD) is a powerful tool for microstructural characterization of crystalline materials. EBSD enables visualization and quantification of the effect of synthesis methods on the microstructure of individual grains, thus correlating the microstructure to mechanical and electrical efficiency. Therefore, this work was designed to investigate the microstructural changes that take place in the Ni-SDC cermet anode under different synthesis methods, such as the glycine–nitrate process (GNP) and ball-milling. EBSD results revealed that different grain size and distribution of Ni and SDC phases considerably influenced the performance of the Ni–SDC cermet anodes. The performance of the Ni–SDC cermet anode from GNP was considerably higher than that of Ni-SDC from ball-milling, which is attributed to the triple-phase boundary (TPB) density and phase connectivity. Due to the poor connectivity between the Ni and SDC phases and the development of large Ni and SDC clusters, the Ni-SDC cermet anode formed by ball milling had a lower mechanical and electrical conductivity. Moreover, the Ni–SDC cermet anode sample obtained via GNP possessed sufficient porosity and did not require a pore former. The length and distribution of the active TPB associated with phase connectivity are crucial factors in optimizing the performance of Ni-SDC cermet anode materials. The single cell based on the Ni–SDC composite anode prepared through GNP exhibited a maximum power density of 227 mW/cm2 and 121 mW/cm2 at 800 °C in H2 and CH4, respectively.

Effect of Sintering Temperature on Microstructure and Mechanical Properties of Hot-Pressed Fe/FeAl2O4 Composite

An Fe/FeAl2O4 composite was prepared with Fe-Fe2O3-Al2O3 powder by a hot press sintering method. The mass ratio was 6:1:2, sintering pressure was 30 MPa, and holding time was 120 min. The raw materials for the powder particles were respectively 1 µm (Fe), 0.5 µm (Fe2O3), and 1 µm (Al2O3) in diameter. The effect of sintering temperature on the microstructure and mechanical properties of Fe/FeAl2O4 composite was studied. The results showed that Fe/FeAl2O4 composite was formed by in situ reaction at 1300 °C–1500 °C. With the increased sintering temperature, the microstructure and mechanical properties of the Fe/FeAl2O4 composite showed a change law that initially became better and then became worse. The best microstructure and optimal mechanical properties were obtained at 1400 °C. At this temperature, the grain size of Fe and FeAl2O4 phases in Fe/FeAl2O4 composite was uniform, the relative density was 96.7%, and the Vickers hardness and bending strength were 1.88 GPa and 280.0 MPa, respectively. The wettability between Fe and FeAl2O4 was enhanced with increased sintering temperature. And then the densification process was accelerated. Finally, the microstructure and mechanical properties of the Fe/FeAl2O4 composite were improved.

Te-Embedded Nanocrystalline PbTe Thick Films: Structure and Thermoelectric Properties Relationship

The Te-embedded PbTe nanocrystallline thick films (i.e., 50 µm) were electrodeposited, where the fraction and average grain size of PbTe and Te phases were tuned by adjusting the applied potential followed by post thermal treatment. The crystal grain boundary and Te nano-inclusion in the films played critical roles in their thermoelectric properties. The Te-embedded PbTe thick film with the average grain size of around 100 nm showed lower energy barrier height (EB = 0.023 eV) than thick films with the average grain size of a few tens of nm (EB = 0.11). Although decrease in the energy barrier reduced the Seebeck coefficient, however, it enhanced the electrical conductivity, which resulted in an increase in power factor (PF). The highest power factor was 183 μw K−2 cm−1, achieved at the energy barrier of 0.023 eV.

On the reduction and effect of non-metallic impurities in mechanically alloyed nanocrystalline Ni-W alloys

Non-metallic contamination is a practically unavoidable byproduct of commercial synthesis processes; however, non-metallic impurities are often overlooked when considering material design and performance of nanostructured materials. Importantly, there is disputing evidence as to whether non-metallic contamination stabilize or destabilize nanocrystalline materials against grain growth. Furthermore, it is unclear if non-metallic contamination has a significant impact on hardness of nanocrystalline systems. In this work, two nanocrystalline Ni-28at%W alloys with different impurity concentrations were produced via mechanical alloying to directly evaluate the effect of contamination on thermal stability and hardness of nanostructured materials. The alloys were isothermally annealed at several temperatures, and the microstructures were compared by applying atom probe tomography and aberration-corrected scanning transmission electron microscopy. It was determined that impurity concentrations can be substantially reduced by using specific milling media and pre-milling reduction processes. Furthermore, the clean and contaminated alloys exhibited similar thermal stabilities against grain growth, but the clean alloy displayed a 100% improvement in hardness despite a similar grain size and distribution of second phases. Impurity phases including CrOx, Ni6W6C, and trapped Ar pores were also identified and likely contributed to the thermal stability and mechanical properties observed in this study. Overall, this work suggests that impurities my not always be detrimental to thermomechanical behavior of nanocrystalline systems.

Synergistic Ground and Orbital Observations of Iron Oxides on Mt. Sharp and Vera Rubin Ridge.

Visible/short‐wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover's traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also has the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported. (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late‐stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity's experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections and the caveats in using these data for geologic interpretations and strategic path planning tools.