Study of Vibration Damping Behaviour of Magnetomechanical Powder Coated Metals and Alloys

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ScienceDirect Materials Today: Proceedings 4 (2017) 8418–8426

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ICAAMM-2016

Study of Vibration Damping Behaviour of Magnetomechanical Powder Coated Metals and Alloys Pakkirappa Ha,*, Mahesha Kb, Sachidananda K B c a

Associate Professor, Mechanical Engineering Department, Acharya Institute of Technology, Bengaluru-560 107, India b Professor, Mechanical Engineering Department, Acharya Institute of Technology, Bengaluru-560 090, India c Assistant Professor, Mechanical Engineering Department, Acharya Institute of Technology, Bengaluru-560 090, India

Abstract

Materials used for engineering applications should be light in weight, anticorrosive, resist wear and shocks. Most of the metals and alloys used in aerospace, marine, defense, sports and structural applications are subjected to mechanical forces. Alloy steels, non-ferrous alloys and other damping materials limit their vibration damping because of their bulky nature. Several researchers have carried out research on reducing the vibration of bulky alloys using various transformation techniques. This paper discusses the damping behavior of various bulk and coated materials. It is evident that damping capacity is due to internal frictions, porosity and magnetic domains of magnetomechanical materials. SEM, XRD and Kerr effect studies have been used to understand surface characteristics and coating quality of the thermally sprayed metals and alloys. In this research work, stainless steel-AISI 304 alloy substrate is powder coated by air plasma spray(APS) method using magneto-mechanical Fe16Cr2Al powder of 99.9% purity. Samples with a coating thickness of 50µm were tested for damping behavior using three point bending method on a dynamic mechanical analyzer. Results were evaluated for damping capacity versus stress/ strain /time and found that there is an improvement in the damping capacity. SEM, XRD images were studied to understand the uniformity in coating, degree of porosity and density of the coating. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility ofthe Committee Members of International Conference on Advancements in Aeromechanical Materials for Manufacturing (ICAAMM-2016).

Keywords: Magneto-mechanical; Damping; Plasma spray; Coating; Stainless steel *Corresponding author. Tel.: +91-80 2255 5555, +91-9448615407. E-mail:[email protected], [email protected]

2214-7853© 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility ofthe Committee Members of International Conference on Advancements in Aeromechanical Materials for Manufacturing (ICAAMM-2016).

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1. Introduction Several large and small scale industries use an array of metals, materials and equipment that are subjected to various conditions such as shocks and vibrations, corrosion and wear. Bulky materials increases weight, material cost and decrease performance. Many industries focused their attention to use protective coatings to increase durability and to protect various metals from vibrations, exterior abrasions, spoilage and reduction of material, manufacturing methods, increased performance and cost.Vibration is a concern in designing of aircraft, structures, electronic appliances, sports utilities, naval equipment and many more, where forces are dynamic in nature. Vibrations are undesirable for the purpose of stability, position control, performance and noise control. This can be reduced by increasing the damping capacity tan δ (loss tangent) or increasing the stiffness (storage modulus).Tan δ is nothing but a ratio of loss modulus to the storage modulus which has to be considered with high importance for reduction of vibration. Researchers [1] stated that dislocations, porosity, grain boundaries, phase boundaries and interfaces contribute to the damping. Due to the application of load, defects may move and the surface may slip during vibration thereby dissipate the energy thus causing the microstructure to affect the damping capacity [2] 2. Literature review 2.1. Vibration damping Vibration damping of materials is classified into five different damping mechanisms such as internal material damping, radiation damping, interface damping (friction damping), energy losses due to reflection at discontinuities of structures, and viscous damping caused by viscoelasticity of material. Internal friction of metals occurs due to the internal microstructure mismatch of the material. The internal friction results from dislocation vibration within the material, the sliding of grain boundary and phase interface, and together with the micro-plastic deformation caused by the difference in coefficients of thermal expansion and elasticity modulus of various phases [3]. Mechanisms influencing the damping properties of metals are multiphase structure, ferromagnetism, dislocation damping and the damping due to movable twin boundaries [4]. All these mechanisms cause hysteretic damping. Some commercially available special ferritic steels like Fe-Cr or Fe-Mn with relatively high damping have been developed. Studies have shown that damping effect depends on two mechanisms such as magneto-elasticity (Fe-Cr steels); reorientation and movement of twins; and twin boundaries (Fe-Mn steels). 2.2. Coating method, materials and their characteristics: Thermal spray is a term used for a group of processes in which metals, ceramics and polymeric materials are fed in the form of powder, wire, or rod to a torch or gun, and are heated to near or above the melting point of the materials at a temperature of 10000-15,000K and velocity of 1 km/sec. The powder melts completely and accelerates particles towards the target [5] and impact of the droplets makes the thin lamellar particles to adhere to the surface, overlaps each other and gets interlocked when they solidified [6]. Damping behaviour of thermally sprayed coatings and that of the cast alloys was found similar for the same chemical composition [7]. Higher annealing temperature or longer annealing time is necessary to attain the same magnitude of the damping capacity as that cast alloys and the damping improvement observed is due to magnetic domain wall movement [8, 9]. Damping capacity of these alloys can be increased by alloying in the form of composite or powder coating on the structural high damping alloys. Therefore, the study on Fe-Cr-X coatings has received much attention in these days as good damping ,high temperature and wear resistant materials. Damping capacity and tensile strength of usual engineering alloys and high damping alloys are higher than 10% [10]. According to the dominant damping mechanisms, high damping alloys can be classified into composite type (gray cast iron and Zn-Al alloy), magnetostrictive type (Fe-Cr, Fe-Al alloys), dislocation type (Mg alloys) and interfaces type (Mn-Cu alloys) [11]. Research on the magnetic properties [12] and the loss capability of Fe-Cr-Al alloys for attenuation of machine part vibrations and an addition of aluminium remarkably increased the damping capacity. Temperature dependence of the flexural damping properties of materials and coatings up to 900 °C is

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studied [13]. Damping behavior of several materials used in thermal barrier coating systems from room temperature up to 1200 °C has been studied and the effect of a platinum modified diffusion nickel aluminide bond-coat and an electron-beam evaporated, the yttria-stabilized zirconia thermal barrier coating has been reported [14]. Researcher [15] studied the surface of titanium alloys at substrate temperatures not higher than 400°C and after deposition of such coatings on the surface of titanium samples for their promising extended service life of titanium blades. Damping properties and dynamic mechanical performance of NiCrAlY coating, AlCuFeCr quasicrystalline coating and nanostructured ZrO2 ceramic coating, which were prepared by plasma spray method were studied and reported that damping capacity (Q−1) of the coated samples have a notable improvement compared to the uncoated substrates[16]. 2.3. Damping behaviour of FeCrAl and coated alloys Many researchers have studied on the bulk materials for their behaviour for vibration damping. Effect of annealing on the vibration damping capacity of high-chromium (16%) ferromagnetic steel and vibration damping capacity of alloys tested [9] using inverted torsional pendulum method, showed that annealing has improved damping and magnetic domain walls movement. Ferromagnetic damping alloys as a group of smart materials have been studied [17] to determine damping capacity and noise energy for wide applications in automobiles, warships, household appliances. Vibration damping in steel compounds discussed about vibration damping mechanisms [18] and the influence of microstructure on the properties of damping. Fe16Cr base alloys, before and after heat treatment were experimented for noise and vibration absorption capacity [19]. The noise damping was evaluated by the level of sound emission after impact and the vibration damping was studied using cantilever device. They have also studied Kerr effect to know magnetic domains. The improvement of vibration damping after heat treatment decreases internal stresses in materials and changes in magnetic domain structures. A similar study has been carried out on chromium-rich ferromagnetic steels [20]to check improvement in damping capacity along with high mechanical strength and corrosion resistance. Mechanism of high damping capacity of high chromium steels, α-Fe and its dependence on some external factors has been discussed [21]. He explored the effect of heat treatment on the maximum capacity of damping about 50 steels and temperatures ranges amplitude critical points connected with the different damping mechanism. Study also revealed the influence of heat treatment on elastic and non-elastic parameters of internal friction of high chromium ferritic alloys and α-Fe steels main structural mechanism 3. Materials and methods In this research, AISI 304 alloy stainless steel is used as substrate material and Fe16%Cr2%Al powder as coating material with Fe of 99.9% purity. The coating powder was mixed according to weight ratios and ball milled for 2 hours to get the homogeneity and uniformity in the mixed powder. Air plasma spray method was used to coat the surface of the substrate. The chemical composition of substrate material used in the experiment is shown in Table1. Table 1: Composition of AISI 304 stainless steel substrate Composition

Fe

Cr

Ni

Mn

C

P

S

Si

Percentage, w/w

66.345

18-20

8-10

2

0.08

0.045

0.03

1

Samples were prepared to (45 x 10 x1.6) mm size for the 3-point bending mode testing on a dynamic mechanical analyzer (DMA).The coating was done on the substrate using plasma spray method for 50 μm thickness. Fig 1 and Fig 2 shows the uncoated and coated samples of the substrate.

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Fig. 1. Uncoated stainless steel substrate

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Fig. 2. Fe16Cr2Al coated stainless steel substrate

3.1. Surface preparation: The substrate surface is roughened by grit blasting for contaminant free, no oil, and no water and for blast media residues. Substrates were roughened by blasting quartz sands of 16-20 mesh at an air pressure of 5 kg/cm2 and standoff distance is 120-150 mm [20, 21]. Substrate samples were cleaned thoroughly with acetone using fine cotton to remove residues. Atmospheric plasma spraying (APS) was done immediately after the cleaning using TAFA Model SG-100 (80 kW) plasma spray torch with a nozzle diameter of 3mm. Argon and Hydrogen are the primary and secondary gases, feed rate of 6-8 gm/cc, the traverse speed of 100mm/sec and pitch rate of 5mm/step were the input parameters used. 3.2. Dynamic mechanical analyzer (DMA)

Fig. 3. (a) Dynamic mechanical analyzer

Fig. 3.(b) 3-point bending fixture

EPLAXOR@500

Vibration damping capacity of samples was tested using EPLEXOR® 500N, NETZSCH GABO Instruments GmbH, Ahlden, Germany. This high-end dynamic mechanic thermal analysis combines with dynamic material testing to determine absolute values of damping modulus as shown in fig. 3 (a) and 3 (b). The various parameters of DMA are force range ± 500N, Dynamic strain is ±1.5 mm (3 mm), strain rate is up to 35 mm, temperature up to 500°C and frequency range is 0.01Hz-100Hz. Input parameters for testing are: static load10N ±0.10N, Dynamic strain (with 0.1%)up to8N ±0.05 (Max), Static strain0.2%, Frequency 0-10Hz.The strain levels are generally maintained within the elastic limit of 0.08%. Maximum strain depends on the sample, clamping device and frequency at which test is conducted.

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4. Results and discussions 4.1. Damping analysis:

Damping Capacity Q-1

AISI 304 Stainless steel subjected to vibration damping using dynamic mechanical analyzer for an uncoated and 50 µm thickness substrate.

Uncoated Coated 50 µm

Stress (dyn), 106 N/m2 Fig. 4. Damping capacity Vs dynamic stress

Vibration damping of metals and alloys is found to be difficult among different materials because they are very sensitive to testing conditions like strain, temperature, strain amplitude, frequency, specimen geometry, stress–field, gripping surface, humidity of the system [21, 22, and 23]. The damping performance of uncoated and 50 µm Fe16Cr2Al coated AISI 304 stainless steel substrates are shown in Fig. 4 to Fig. 6. Fig.4 shows the variation of damping capacity with dynamic stress. It is observed that there is an increase in damping capacity of the coatings by 62.95% ±5.80 with an increase in dynamic stress. Dynamic stress is observed is due to the presence of the cyclic load. Further, results showed that the damping capacity of the coatings had more dependency on strain amplitudes. The damping capacity of coated samples increased by 64.30±4.67 as the strain amplitude increases as shown in Fig. 5. The magnitude of the shear stress at the interface of the splats is sufficient to overcome frictional loads. These micro-slips at the interface of diffused alloy are likely to occur due to dislocation and attributes to the frictional energy loss [2].

Damping Capacity Q-1

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Uncoated

Strain (dyn) in %

Damping Capacity Q-1

Fig. 5. Damping capacity Vs dynamic strain

Uncoated

Time in Seconds Fig. 6. Damping capacity Vs time

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Fig. 6 shows the variation of damping capacity with time. It is found that in a time sweep mode of testing, the damping values were increasing with time. Damping capacity increases by 60.74±3.19 with respect to time. Damping values were exponentially increasing in all the cases due to increased thickness as observed in iron chromium base coatings [7] and also due to reduced porosity. Q-1 increases by 60% above in all cases of 50 µm coating with respect to the uncoated substrate.

Fig. 7. SEM micrographs of Fe16Cr2Al coated 50µm AISI 304 substrate

4.2. SEM and X-Ray diffraction: FeCrAl coating X-ray images shown in Fig.8 were studied for the composition seen as peaks and original powder to the lost powder during spraying. Formation of oxides on the surface, Fe peaks and Al peaks cannot be seen above the background noise. The small amount of oxide is detected by XRD images. FeCrAl coatings exhibit Cr and CrFe4 peaks in addition to the Fe peaks whereas oxide is also not detected [21, 24]. XRD graph of the coating substrate appears to be amorphous nature because there are no distinct peaks for various elements of the coating. Aluminum iron oxide peaks are seen along with few ferrite peaks. But there are no distinct chromium oxides of the coating. SEM images were taken for studying the melting level of mixture, splat, porosity, unmelted powder, depth of coating.SEM images show that the coating is dense with fewer pores and unmelted particles. The range of standoff distance is 120-150 mm. whereas smaller standoff distance leads to more porosity but larger standoff distance leads to resolidification of melt thereby causing less porosity [25]. SEM images of plasma spray coatings consist of many layers of thin, overlapping lamellar particles called as splats which are shown in Fig.7. Generally, higher velocities of particle coating produce better bonding and denser coatings, such as cohesively (splat-to-splat) and adhesively (coating-to-substrate). Rapid quenching of the particles on impact is 106 to 108 °C/s is metastable for metals resulting in grains within the splats to submicron-size or even amorphous. The coating is uniform because of the interaction between the powder and the substrate at very high temperature and that the strength of materials decreases with an increase in porosity [26]. Porosity is the volume defect which cannot be avoided during coating, which produces higher damping in engineering metals [23, 27]. Low porosity produces compact coatings and to substrate without gaps or cracks [28]. The average damping capacity increases approximately by 60% with an increase in porosity from 5% to 10%.

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Fig. 8.X-Ray diffraction image of Fe16Cr2Al coated 50µm AISI 304 substrate

5. Conclusion   

Magneto mechanical powder coated steel alloy exhibited the increase in the vibration damping in all the cases measured with respect to stress, strain and time compared to uncoated samples. As the coating thickness increases the damping capacity also increases SEM and XRD images revealed that porosity which exists helps in increasing the damping capacity of the coated material.

Acknowledgement Authors are thankful to AICTE, New Delhi for sponsoring to conduct research work on these magnetomechanical coated alloys and Spraymet Surface Technologies Pvt Ltd. Bengaluru, India, for coating the samples.

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