title: Study of Titanium based Composite Coatings for Resistance against Molten Aluminium Soldering on H13 Tool Steel

authors: Salman, Asma Siddiq

subjects: mechanical milling

abstract: The service life of industrial components is limited predominantly by chemical corrosion, mechanical failure or mechanical wear. In the aluminium high pressure die casting industry, liquid aluminium is extremely reactive with the constituents of H13 die steel and has a tendency to form intermetallic layers. This chemical interaction results in sticking of molten metal to the die surface which produces defective castings and also damages the die surface. The use of thermal spray coatings provides protection to the surfaces operating in severe environments. An HVOF thermally sprayed coating has the advantage of having excellent bond strength and very low porosity levels (< 1%). This research work is concerned with producing and evaluating the performance of titanium/alumina based composite coatings to improve the service life of tool steel (H13) used for dies in aluminium high pressure die casting and dummy blocks used in Al extrusion.
In this research work, the powder feedstocks for making the composite coatings were produced by high energy mechanical milling of a mixture of Al and TiO₂ powders in two different molar ratios followed by a thermal reaction process. The feedstock powder was then thermally sprayed using a high velocity oxygen fuel (HVOF) technique on H13 steel substrates to produce Ti(Al,O)/Al₂O₃ and TiAl/Al₂O₃ composite coatings. The performance of the coatings was assessed in terms of Al soldering, liquid metal corrosion resistance, thermal shock resistance and wear resistance.
In an immersion test, the coated specimens were dipped into molten Al at a temperature of 700 ± 10 °C for different intervals of time. The performance of the coatings was tested in terms of liquid metal corrosion resistance and propensity to Al soldering. The dissolution behaviour of the coatings was evaluated by measuring weight loss after dipping the samples in to molten aluminium. The immersion test results showed that the coated samples have relatively few locations where aluminium soldering (reactive/chemical) occurred, however, an H13 steel surface showed more tendency for aluminium soldering. It was found that composite coatings changed the molten Al attack on H13 tool steel from a generalized to a localized one. No reaction between molten aluminium and a Ti(Al,O)/Al₂O₃ composite coating was identified. The TiAl/Al2O₃ composite coating was found to be attacked by molten aluminium as a result of a reaction between the coating and molten aluminium. The metallic phase TiAl in the composite coating is believed to be attacked by the molten Al. A Ti(Al,O)/Al₂O₃ composite coating was found to be a better protective coating than the TiAl/Al₂O₃ composite coating due its stability against molten aluminium attack.
The thermal shock behaviour of the composite coatings was investigated by subjecting the coated coupons to a number of cycles, each cycle consisting of a holding time of 30 seconds in molten aluminium at 700 ± 10 °C followed by quenching into water. The surfaces of the coupons were examined for Al soldering and an evaluation of surface spallation. Any cracks found in the coatings were studied to explain their thermal shock behaviour. A Ti(Al,O)/Al₂O₃ composite coating on H13 tool steel produced from a fine feedstock has better thermal shock resistance than the Ti(Al,O)/Al₂O₃ TiAl/Al₂O₃ composite coatings produced from the agglomerated feedstocks.
The study also describes and compares the tribological properties such as friction and sliding wear rate of the composite coatings both at room and high temperature (700.°C) under dry and lubricating conditions. The wear resistance of the coatings was investigated by a tribometer using a spherical ended alumina, flat ended high speed steel and spherical ended hardened steel pins as counter bodies. The experimental results show that the composite coatings look promising for high temperature applications due to their low wear rate at high temperature. However room temperature applications of the composite coatings can be improved under lubricated conditions.
Successful trials of a Ti(Al,O)/Al₂O₃ composite coated dummy block revealed that the coating has potential as an industrial coating.

text: Study of Titanium based Composite Coatings for Resistance against Molten Aluminium Soldering on H13 Tool Steel The service life of industrial components is limited predominantly by chemical corrosion, mechanical failure or mechanical wear. In the aluminium high pressure die casting industry, liquid aluminium is extremely reactive with the constituents of H13 die steel and has a tendency to form intermetallic layers. This chemical interaction results in sticking of molten metal to the die surface which produces defective castings and also damages the die surface. The use of thermal spray coatings provides protection to the surfaces operating in severe environments. An HVOF thermally sprayed coating has the advantage of having excellent bond strength and very low porosity levels (< 1%). This research work is concerned with producing and evaluating the performance of titanium/alumina based composite coatings to improve the service life of tool steel (H13) used for dies in aluminium high pressure die casting and dummy blocks used in Al extrusion.
In this research work, the powder feedstocks for making the composite coatings were produced by high energy mechanical milling of a mixture of Al and TiO₂ powders in two different molar ratios followed by a thermal reaction process. The feedstock powder was then thermally sprayed using a high velocity oxygen fuel (HVOF) technique on H13 steel substrates to produce Ti(Al,O)/Al₂O₃ and TiAl/Al₂O₃ composite coatings. The performance of the coatings was assessed in terms of Al soldering, liquid metal corrosion resistance, thermal shock resistance and wear resistance.
In an immersion test, the coated specimens were dipped into molten Al at a temperature of 700 ± 10 °C for different intervals of time. The performance of the coatings was tested in terms of liquid metal corrosion resistance and propensity to Al soldering. The dissolution behaviour of the coatings was evaluated by measuring weight loss after dipping the samples in to molten aluminium. The immersion test results showed that the coated samples have relatively few locations where aluminium soldering (reactive/chemical) occurred, however, an H13 steel surface showed more tendency for aluminium soldering. It was found that composite coatings changed the molten Al attack on H13 tool steel from a generalized to a localized one. No reaction between molten aluminium and a Ti(Al,O)/Al₂O₃ composite coating was identified. The TiAl/Al2O₃ composite coating was found to be attacked by molten aluminium as a result of a reaction between the coating and molten aluminium. The metallic phase TiAl in the composite coating is believed to be attacked by the molten Al. A Ti(Al,O)/Al₂O₃ composite coating was found to be a better protective coating than the TiAl/Al₂O₃ composite coating due its stability against molten aluminium attack.
The thermal shock behaviour of the composite coatings was investigated by subjecting the coated coupons to a number of cycles, each cycle consisting of a holding time of 30 seconds in molten aluminium at 700 ± 10 °C followed by quenching into water. The surfaces of the coupons were examined for Al soldering and an evaluation of surface spallation. Any cracks found in the coatings were studied to explain their thermal shock behaviour. A Ti(Al,O)/Al₂O₃ composite coating on H13 tool steel produced from a fine feedstock has better thermal shock resistance than the Ti(Al,O)/Al₂O₃ TiAl/Al₂O₃ composite coatings produced from the agglomerated feedstocks.
The study also describes and compares the tribological properties such as friction and sliding wear rate of the composite coatings both at room and high temperature (700.°C) under dry and lubricating conditions. The wear resistance of the coatings was investigated by a tribometer using a spherical ended alumina, flat ended high speed steel and spherical ended hardened steel pins as counter bodies. The experimental results show that the composite coatings look promising for high temperature applications due to their low wear rate at high temperature. However room temperature applications of the composite coatings can be improved under lubricated conditions.
Successful trials of a Ti(Al,O)/Al₂O₃ composite coated dummy block revealed that the coating has potential as an industrial coating.

year: 2011

title: Physiological effects of aluminium in relation to diel pH changes on fish and kōura

authors: Fensham, Emily

subjects: Physiology

abstract: Alum (aluminium sulphate, Al₂(SO₄)₃) dosing is used to reduce eutrophication of lakes by sequestering phosphorus and preventing its uptake by phytoplankton for growth. When applied to water at circum-neutral pH, alum forms aluminium hydroxide (Al(OH)₃), a precipitate that is benign at environmentally relevant concentrations and moderate concentrations. However, at low and high pH, dissolved ionic aluminium species evolve which are known to be toxic to a range of aquatic organisms. In the Rotorua lakes, alum dosing occurs under circum-neutral pH (6–8) conditions, however, transiently elevated pH (10) conditions may occur due to algal uptake of carbon dioxide (CO₂) for photosynthesis. Under elevated pH, particulate Al(OH)₃ solubilises to form aluminate (Al(OH)₄⁻), which can interfere with osmoregulation and respiration. Similarly, at circumneutral pH, solid Al(OH)₃ predominates and is generally benign, but in high concentrations can irritate and damage gill tissue causing inflammation and excess mucus production which impairs oxygen uptake, CO₂ elimination, and ultimately causing death. The effects of aluminium under intermittent elevated pH on fish gill function, respiration rates, and metabolism have not yet been investigated.

This study investigated the impacts of aluminium on rainbow trout (Oncorhynchus mykiss), common bully (Gobiomorphus cotidianus), and kōura (Paranephrops planifrons) osmoregulation and respiration under diurnal pH cycles, through two experiments. The first being a dose exposure study whereby rainbow trout and kōura were exposed to alum derived aluminium at 2 mg L⁻¹ under diel pH cycling (pH 7–10) over 10 days. Measured parameters included haematocrit, haemoglobin, mean cell haemoglobin concentration (MCHC), and blood plasma osmolarity in rainbow trout and haemolymph osmolarity in kōura. A significant increase (Student’s t-test, P <0.05) in the mean cell haemoglobin concentration (MCHC) in the rainbow trout control group indicated erythrocyte swelling, suggesting a generalised stress induced response. However, other haematological variables such as plasma and haemolymph osmolarity, haematocrit and haemoglobin concentrations were not significantly different (Student’s t-test, P >0.05) between control and treatment groups. Histological examination of kōura and rainbow trout gill tissue was also conducted, with abnormalities observed within both the control and treatment groups for each species. However no significant differences (Kolomogorov-Smirnov, P >0.05) were observed between groups. It was concluded that organisms can physiologically compensate for aluminium induced stress and disturbance at the gills.

A second experiment utilised intermittent flow respirometry to determine mass specific metabolic oxygen consumption rates (MO₂) of rainbow trout, common bully, and kōura exposed to 2 mg Al L⁻¹ and diel pH fluctuations (pH 7–10) over 60 hours. It was expected that precipitation of dissolved aluminium onto the gill surface during pH transitions and/or binding of dissolved aluminium species would inhibit the respiratory gas exchange resulting in increased gill ventilation from hypoxic and hypercapnic conditions. There was a significant negative correlation (Pearson’s, r² = 0.34, P <0.0001) between pH and MO₂ possibly indicating kōura are sensitive to the experimental conditions. However, there were no consistent trends in differences between control and treatment groups for any of the tested species. Data interpretation was hindered by the necessity to exclude samples from the rainbow trout and common bully control groups due to aberrations in the oxygen sensor data. However, mean MO₂ was within expected ranges for rainbow trout and kōura, indicating that significant respiratory impacts were not occurring within the period of exposure. Although definitive conclusions could not be made regarding changes to MO₂ in response to aluminium and diel pH cycling, it is unlikely that acute impacts would result from these conditions in the natural environment.

From this research it is concluded that the combined impacts of aluminium and diel pH cycling are unlikely to cause acute osmoregulatory or respiratory impairment or cause death in kōura, common bully, or rainbow trout.

text: Physiological effects of aluminium in relation to diel pH changes on fish and kōura Alum (aluminium sulphate, Al₂(SO₄)₃) dosing is used to reduce eutrophication of lakes by sequestering phosphorus and preventing its uptake by phytoplankton for growth. When applied to water at circum-neutral pH, alum forms aluminium hydroxide (Al(OH)₃), a precipitate that is benign at environmentally relevant concentrations and moderate concentrations. However, at low and high pH, dissolved ionic aluminium species evolve which are known to be toxic to a range of aquatic organisms. In the Rotorua lakes, alum dosing occurs under circum-neutral pH (6–8) conditions, however, transiently elevated pH (10) conditions may occur due to algal uptake of carbon dioxide (CO₂) for photosynthesis. Under elevated pH, particulate Al(OH)₃ solubilises to form aluminate (Al(OH)₄⁻), which can interfere with osmoregulation and respiration. Similarly, at circumneutral pH, solid Al(OH)₃ predominates and is generally benign, but in high concentrations can irritate and damage gill tissue causing inflammation and excess mucus production which impairs oxygen uptake, CO₂ elimination, and ultimately causing death. The effects of aluminium under intermittent elevated pH on fish gill function, respiration rates, and metabolism have not yet been investigated.

This study investigated the impacts of aluminium on rainbow trout (Oncorhynchus mykiss), common bully (Gobiomorphus cotidianus), and kōura (Paranephrops planifrons) osmoregulation and respiration under diurnal pH cycles, through two experiments. The first being a dose exposure study whereby rainbow trout and kōura were exposed to alum derived aluminium at 2 mg L⁻¹ under diel pH cycling (pH 7–10) over 10 days. Measured parameters included haematocrit, haemoglobin, mean cell haemoglobin concentration (MCHC), and blood plasma osmolarity in rainbow trout and haemolymph osmolarity in kōura. A significant increase (Student’s t-test, P <0.05) in the mean cell haemoglobin concentration (MCHC) in the rainbow trout control group indicated erythrocyte swelling, suggesting a generalised stress induced response. However, other haematological variables such as plasma and haemolymph osmolarity, haematocrit and haemoglobin concentrations were not significantly different (Student’s t-test, P >0.05) between control and treatment groups. Histological examination of kōura and rainbow trout gill tissue was also conducted, with abnormalities observed within both the control and treatment groups for each species. However no significant differences (Kolomogorov-Smirnov, P >0.05) were observed between groups. It was concluded that organisms can physiologically compensate for aluminium induced stress and disturbance at the gills.

A second experiment utilised intermittent flow respirometry to determine mass specific metabolic oxygen consumption rates (MO₂) of rainbow trout, common bully, and kōura exposed to 2 mg Al L⁻¹ and diel pH fluctuations (pH 7–10) over 60 hours. It was expected that precipitation of dissolved aluminium onto the gill surface during pH transitions and/or binding of dissolved aluminium species would inhibit the respiratory gas exchange resulting in increased gill ventilation from hypoxic and hypercapnic conditions. There was a significant negative correlation (Pearson’s, r² = 0.34, P <0.0001) between pH and MO₂ possibly indicating kōura are sensitive to the experimental conditions. However, there were no consistent trends in differences between control and treatment groups for any of the tested species. Data interpretation was hindered by the necessity to exclude samples from the rainbow trout and common bully control groups due to aberrations in the oxygen sensor data. However, mean MO₂ was within expected ranges for rainbow trout and kōura, indicating that significant respiratory impacts were not occurring within the period of exposure. Although definitive conclusions could not be made regarding changes to MO₂ in response to aluminium and diel pH cycling, it is unlikely that acute impacts would result from these conditions in the natural environment.

From this research it is concluded that the combined impacts of aluminium and diel pH cycling are unlikely to cause acute osmoregulatory or respiratory impairment or cause death in kōura, common bully, or rainbow trout.

year: 2022

title: Informed consent in the Aotearoa New Zealand context

authors: Cargo, Tania

abstract: Psychologists are in very privileged positions; we use our clinical, community, academic, and research skills to support individuals, families, and communities, often during extremely vulnerable times in their lives. Psychologists have specific duties and responsibilities to not only offer a competent and ethical service, but to ensure that clients have been engaged in an open and honest process of gaining informed consent before a psychological service is offered, and either accepted or declined by the client (Knapp, Gottlieb, & Handelsman, 2015; Nagy, 2011).

text: Informed consent in the Aotearoa New Zealand context Psychologists are in very privileged positions; we use our clinical, community, academic, and research skills to support individuals, families, and communities, often during extremely vulnerable times in their lives. Psychologists have specific duties and responsibilities to not only offer a competent and ethical service, but to ensure that clients have been engaged in an open and honest process of gaining informed consent before a psychological service is offered, and either accepted or declined by the client (Knapp, Gottlieb, & Handelsman, 2015; Nagy, 2011).

year: 2016